All Small Six Help! Did I just screw up my new build?

[Frank]

But what if you’re rear’s don’t lock up and there is more braking power still left in them BEFORE they lock up? You will never know without being able to adjust.

If the pedal is mashed hard enough, wheels are going to slide. If all 4 slide simultaneously there is no more braking power, and no need for changing the pressure front to rear. . . or so it seems to me, but I've never had a sports car or tested the limit of my braking ability (intentionally) so I'll step back quiet now.

 

[DON]

If the pedal is mashed hard enough, wheels are going to slide. If all 4 slide simultaneously there is no more braking power, and no need for changing the pressure front to rear.

True!
All I’m saying is if they don’t.
Also if you upgrade wheel cylinder in the rear like I did, one could have max braking with less pedal pressure. Which would take adjusting for max braking.
60’s vintage brake systems are pretty primitive compared to today’s systems, they can be easily upgraded but upgrades to the entire system help. Adjustable brake balance is just one factor.
I like to keep the corners square on brakes and tires

 

[Otto]

@Otto thank you for the suggestion!
Would it be easier to remove fenders for door adjustment? I don’t think I can reach door hinge bolts with the door closed lol
I was thinking to put the door, try it, remove, adjust…and repeat. But seems like it might be a very long process, especially that I had to put new door hinges

No need to remove fenders. If Mustangs are like Falcons, the hinges bolt to the body from the inside out, so you'll have to remove the kick panel but the bolts should be easily accessed. Sometimes there will be paint marks or other clues as to where the hinges were located. Just get close to those marks as a starting point and adjust from there. If you have better marks to go by on the body, maybe try bolting hinges to the body first and then door to hinges. Or the opposite if there are better marks on the door.
Just be careful the door is not too far forward to start- so you don't catch the fender edge. If you remove the striker from the jamb, it should go pretty quickly. Just be careful to not chip anything and you should be fine.
UAW workers did this in seconds!

Edit: I just looked at the photos you posted close up and the hinges are bolted to the body from the outside; forget what I said! Falcons and Mustangs are not always the same! I have a special 1/2" wrench for hinge work like this, but it's not impossible without it.
In your case, I would bolt the hinges to the body first matching up where the old hinges attached closely (maybe slightly rearward so you don't catch the fender). Leave the bolts snug but less than fully tight so you can move them around once the door is attached and adjust from there. Once you get it perfect, fully tighten and re-install and adjust the striker.