hydroboost uses power steering pump to make power brakes
7'' vac booster is the biggest you can put under the floor
as for heat... not an issue as highsider stated
my 58 truk has 27,000 miles without an issue
as do all 55-59 trucks, seeing as the stock location is under the floor boards
like highsider's pic shows the exhaust can be under the frame and still above the steps
i ran mine similar to his but twice as often
read my build to see more about the hydroboost i installed