I have been running a big block in my 55 since 1970, I don't have a power brake setup but have never had a problem with the manual brakes in all that time. The truck carried an 8 ft camper in the hot Texas summers for 3 yrs with no trouble.
I am using the Chevelle headers, and have modified the pipes on the 2 back cyls to clear the stock steering box. With the truck headers, which I have also used,
I didn't want to make any mods to the frame because the truck is a Cameo and not very common.
You would have even more separation between the booster and the pipes because the truck pipes drop lower than the car headers.
I am planning to put my power brake system in the underfloor location when I change back to a 2wd from its present 4wd setup.
Bob


55 Cameo 396 TH 400 with overdrive
65 Caliente conv
67 BB Caliente conv
67 Mercury 1 Ton
76 GMC 3/4 ton 454ci
84 Buick Turbo Regal