You've heard of a lot of people using the 4 bolt front suspensions and not having problems.
1. What year are the cars, after 1967 Ford only made one spindle for Drum Brakes and 1 spindle for discs, it didn't matter which hub was used, so those spindles are all bent8 quality and yes they would work, but the drum brakes are mucho tiny
2. How do they drive the cars? Speed Racer or old Lady going to church on Sunday that's owned the car since it had 2 miles on the odometer (and now it's up to 12,000k after 45 years)
If you can find one of those people with original 6 cylinder spindels on the early cars (pre '67) ask them how fast they stop. From any speed.
FWIW, I've put a 302 into my '67 Mustang that orignially had a 200 and it bolted right in, the only things I had to change was the frame mounts, radiator, throttle linkage, fuel line plumbing, wiring. I never drove it though, I later gave the bent8 to my younger brother and the next motor that car receives will be a 250.
-ron