UPDATE:
So Feets talked me down and into the 1 inch master.
this got me into researching chevy master cylinders. Apparently they wire them backwards, so my brakes have been wrong this whole time.

I put the lines in like you would a mopar. Rear port to the front brakes but they do front to front.

I found they made a 1 inch for manual brakes and managed to find one in garland.
BUT apparently the aftermarket master I have only used 3/8th ports for the front and back. The factory used 1/2 inch for the front and 9/16th for the rear.
I spent all day searching for an adapter. All the parts stores adapter bins are either empty, misfiled, or just full of junk parts people tossed in them. No inventory control on them at all.

However my luck held out today on so many things, wrecks, speed traps, etc.. that at 8, one of the o'riely's happened to have the adapters I needed.

I just finished putting it back together and I can lock up the brakes if I stand on it. but otherwise normal braking.

so 2 different things using an aftermarket manual to power conversion.
wrong master cylinder size and front port to front brakes makes a huge difference.

I still think I can bolt up a 95 intrepid booster and master to the brackets I have, but as long as this booster holds up I will let it go. I might hunt one down next time I go to the yards, or have feets see if he can find one next time he is in the yards. but it works now.

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I had the 10 inch discs from an m-body on the 65 coronet.
feets gave me a set of the 11 inch caliper adapters and I stole the 11 inch discs from him when he sold the hot rod.
so those rotors have been sitting bare on a shelf for several years and at least 6 months or so on my garage floor.

I got a chance today to swap them out. didn't open anything up, just popped the calipers off, swapped the adapters and rotors and then put it back together.

pumped it up till I got a firm pedal again. (had to push a piston back in) and then tried to pull it out of the garage.
had my foot in it standing on the pedal and it wouldn't stop under power. when I put it in neutral it stopped.

I got it on level ground and it won't stop in drive. It will hold in reverse, unless I am on an incline. and of course it stops when I am in neutral.

I tried to drive it with the brakes on a bit, back and forth and it might have helped a little, but hard to tell.

did I miss something? glazed rotors?

I was very careful not to get grease on anything. I changed gloves and everything between setting the bearings in and mounting the rotor. But I will probably spray it down with brake cleaner later just in case.

I did the same swap in my 68 Dart conv with power brakes. Worked fine. Actually couldn't tell much difference at all.

Maybe Feets sprayed the rotors with something to keep em from rusting (I've done that). I'd jack the front wheels off the ground & pull the tires/wheels and have a helper work the pedal as you visual both front corners for anything that dont look kosher. Then I'd replace the wheels and spin em (forward) by hand as the helper works the pedal & see what you discover

10" to 11"???? Are we talking about the 10.87" rotors to the 11.75" rotors ?

Whatever...

Think of it as a lever and you've just lengthened that lever by about 10%. Braking should have improved "slightly". Since it hasn't, I'd be looking for the cause somewhere else in the system.

read it as 'took them off' meaning unhooked everything. probably 'my bad'!

I didn't open anything up. no way is there air in the lines.

these are "new" ish calipers, from when I put in the 10.87's a few years back.

I will take them apart again and see if I put something together wrong. might run some sand paper over the rotors just incase.

Replaced the calipers in my B300 with rebuilts (one proper Mopar, one generic) about a year and a half ago, and when the temp falls below -20C (-4F) the generic leaks just sitting there overnight. Fluid runs out and down the tire. Looks like a small critter took a whiz under the tire in the snow.

Almost wonder if a caliper is hanging up?

Not sure if you have pin or slider type. But assume slider since that is what an M body would have. The slider type has been known to wear on the adapter and cause a hang up, how did the slider ways look?

no mention of new pads?..old pads with new rotors most likely did not burn to each other..

yeah, the slider type.
They seemed to move freely. I didn't notice any wear on the adapters, or the calipers that would stop them from moving.
it does feel like it has hit some limit though. no matter how much harder I press, it doesn't seem to be stopping any more.

nope, reused the old pads. Didn't really think about it. They really don't have many miles on them.

I did use new bearings though. lol.

(1) no air (2) only the L/R front corner assys were changed. (3) same pads (4) I'd brake kleen the pads/calipers (5 grab helper for the pedal (6) visual as he works the pedal (7) compare the old rotor(s) finish to the new rotor(s) finish (tho I dont think that if they are clean) (8) all that is left is a caliper piston travel problem from the retraction (mighta messed up the square seals) but both (L/R corners) appear to be fubared as it ain't pulling to one particular side. unless the retracting messed up both of em. Andrew holler how it turns out

so I pulled it out this morning. It no longer seems to be unable to stop.
it still has a bit of the old problem where it doesn't stop soon enough, or lock up.

I took off the master cylinder to see if the rod had backed down but it was still adjusted.
pedal has more movement without the master bolted up, so no binding there, nor is it the booster.

have never seen it, but can a master be bad and not move farther? or is it only the bleed by, which I have seen in the past?

I will start tearing into the brakes again to see if they are binding up somewhere.

is there a torque spec for the slider bolts? I just cranked down till they stopped.
never been a problem before, but just wanted to make sure.

took both sides apart. cleaned them again, took off some of the pad so it was "flat" again, incase it has molded to the old rotors.

with the pads off, and the sliders tighted down, I verfied I could move the calipers without any binding.

They are better, but about the same as the old set.

I think I have some other issue. If a master can give partial braking without moving further, or it could just be as simple as a bad booster again.

I cannot push hard enough to lock up the brakes, or get it to grab harder.
I literally was standing with both feet on the pedal and the car was still moving.
I think this is unrelated to the new rotor swap, as it did this before and I thought this might sort it out. but it didn't.

I would get a psi gauge and check your pressures at the calibers.
If your up around 1000+psi, then I would say glazed pads and rotors.

How old are your hoses?

anyone know shops that carry that kind of tester? I can't seem to find a parts house that carry's one.

The hoses are about 7 years old. maybe. replaced them with the original disk brake swap.

The reason I asked is the hoses can go bad internally and not show any signs of leaks.