78 Camaro = fat heavy car,lose some weight. I put a T400 in my 80 Camaro because the T350 came apart twice. Put taller tires on the car and see how that works for you(borrow them for a day) A muncie,plus heavy leaf spring car plus 10 bolt diff plus burn outs === expensive. count on breaking spider gears,wheel hop is a possibility, The muncie will break on occasion if you dont upgrade the case.
The car is too heavy so most of the parts will eventually break,including the clutch.
How did you arrive at the 400 horse power figure?