i've used those exact lifters in unbushed blocks a number of times and have never experienced the type of problem you describe.
basically you have a bunch of "controlled" leaks, (i.e. oil to the roller and pushrod oiling.)it's not likely your uncovering the oil gallery, but did you check when installing the lifters? what was your measured lifter to bore clearance during installation? without that information, one could only guess at where the problem may be IMO. is it time for a better pump? the dual line is great, but is the pump itself capable of supplying the volume you need? the dual line is on the INPUT side of the pump, not the OUTPUT.
my guess is that in order to actually fix the problem, you'll have to start investigating all area's of the oiling system and critical dimensons and clearances.

Lots of good ideas here but, I didn't see anyone suggest looking at the oil PRV circuit...It may be a simple solution. I know noone has problems with Milodon pumps... ...but every once in a blue moon something can go wrong. It'd be simple enough to check anyway.

Is there possibly a diamond shaped stamp on the block number pad denoting .008 oversized lifter bores? (I would hope not on a mega block, but...)

Verify the gauge, check it agianst another known accurate gauge BTW what is your idle speed?

Cab the idle speed is around 12 and 1300

Is this a aluminum block?

Nope its steel

Last season before a roller lifter went out and got in my oil pump. With the Indy single line pump(with 2 washers on the pressure spring) and dragster pan I had 80 lbs @ idle Hot & Cold when you revved the engine it would go up to 100 lbs.

So my question is have you took your pickup out and checked it? I had cleaned my oil pan before,but never took the pickup out. Could something be blocking some of the opening?

I hope to get my heads back in a few days. I have already made a mistake before I start back on the engine. I was sure my engine did not oil thru the lifters and push rods,but it does.

It would be nice if all of us could make a list of things to check are do before building our engines. I know I had rather spend a little more time and money now than have to go back later hunting things to fix.

Yes the pickup has been takin out and cleaned thourghly when i had it apart this winter..

SC30 , i have the same set up as you . also had the same issues as you're having , i got there in the end as i'm sure you will , get the motor on the engine stand & figure where the excessive leak down is & i'm sure you'll fix the problem , when you prime the motor it should all come clear.

As i said previously in this post , the oil pump mod netted an increase in oil pressure of around 10/15psi.

Good luck.

my 500ci and indy sr heads was doing the same thing 75psi cold and 10psi hot i used holley jets to restrict the oil flow to the rocker shafts have good oil psi now