I have a 70 dart, wanting to switch 10' drum to disc would like to go LBP and maintain the stock track width?what are my choices? With the SSBC kit from what I understand has a choice between SBP or LBP BUT does the track change ? The stock KH system {stock track} is SBP limited future potential wheels/tires $$

I believe there is a mod you can do with Mustang rotors. Mustangs used a KH brake setup from the factory and had a larger bolt pattern. You have to machine the inside of the rotor for the Mopar sized bearings I think. The Ram Man was offering this service at one time but it was pretty expensive. I would not deal with him. I know there are posts about this on FABO. Maybe do a search there.

Also, I believe Wilwood sells a conversion kit that uses the stock drum spindles. This might be the large bolt pattern. Not sure.

Yes the early mustang rotor that is modified to go onto the SBP 10" drum spindle is the only affordable way to keep the track width the same in the front. There are links out there that show what needs to be machined, or buy the SSBC kit because that is the rotor used.

The big question to the OP is what are you going to do about the rear change over? ESPECIALLY if you are changing this in a Dart/ Valiant body, because the switch to LBP on the rear will also widen the rear track ... unless you can find an NS1/obsolete pair of 66-69 B body 10x 1.75 brake drums.

Wilwood makes a kit for that.
My friend and I put it on his 69 dart.

Track includes wheel offset, correct it with the proper wheel backspace.

there was a (related) thread on this yesterday & iirc the SBP discs have the same track as the SBP drums so this is what I was thinking, if you had SBP discs (I'm sure it'd be cheaper than the other (SBP) disc options, you could look at the SBP rotors (front & back sides) & see if there is room to redrill em to 4.5" which is only 1/4" outward at any point on the circle perimeter from the center and you'd be going to 1/2" wheel studs. if all good on that potential you could drill the 5 new holes on your drill press & a tap is cheap as is thread in 1/2" wheel studs. If that becomes a go holler & I will give you the simple math to locate 5 pinpoint marks to do your drilling. LBP wheel registers (center hole) are larger so you'd just need lug centric lug nuts

John yes going on dart. Thanks for pointing out potential rear/drum issue, as I can`t go any wider... Hummm. May have to just stay with SPB and convert front to KH. Just hate committing that much dollars for the restriction to SBP for future {limit wheels tires}.

use 73 up a body stuff was articles in mag's yrs ago
on mopar action tech archives in depth article

I used the upper arms with big ball joints and all the other stuff off of a 74 valiant for my change over. Worked well. Make sure you get the correct proportioning valve off the disc car.

I have F70-14's on stock 5.5 steelies in the back of my 69 and with the original worn springs it has I can't jack the rear of the car up under the rear axle to change a tire because the tire won't clear the wheel opening lip.

Wider track in the front would actually help because the same tire hits the frame rail before the steering linkage hits the mechanical stop.

The suggested 73 up disc system increases the track width by 7/8 of an inch both sides which wont work with my present size tire and rim which is 235/60r14 on 14x7 Al rim 245/60 on rear . I dont like the wide front look of the 73 up`s

Well then your choice is to buy the stock KH set up and Mustang rotors and modify them or buy the SSBC, or Wilwood, setup ... $$$$$$

Then deal with the rear ... custom offset axles that mimic the SBP axle offset and opening up the lug holes and the center register of the stock rear drums and have the drum balance checked after machining ...

The Mustang rotors use the SAME bearings with a slightly different spacing. From everything that I have seen it takes a spacer in the Mustang rotor to fit the Mopar spindle. Take a close look at all the parts that come with the SSBC kit. In the end, you might find the SSBC kit will not cost much more than finding all the original K-H parts and rebuilding them.

I used a stock set up(upper and lower A arms, spindles, rotors, calipers and ball joints) off a 1973 and later V8 A body disc brake cars on my 1970 Duster to replace the 4 piston Kelsy Hays set up to avoid drilling the stock rotors to get the bigger bolt pattern They stopped way better than the OEM brakes did That was non power brakes also on both cars Not sure about the track width differences, I used a set of skinny (4.5x15)front rims and VW 165x15SR tires

Moser will make BBP axles with the correct spacing to use the 1.75" brakes, and will redrill your drums.