I had the same problem with the three bolts to four bolts, as for clearence I have a sbc with custom headers that left maybe an inch of space if that when I mocked the thing up, I presume you mean your problem is the rib on the firewall and the three bolt to four bolt, , the rib can be taken...
I have a 77 brake booster and master cylinder, Works, I ended up using a toyota tundra booster (more power!), I had the original single cylinder 69 master cylinder, then I went up to the tundra cylinder and picked up the 77 booster the day prior, funny how the world works out, Figure out what a...