65 Mustang hp increase?
Wheelbarrow full of $100 bills, and "slick ("performance parts") salesman", - plus a willing mechainc!
You can make it go like a "scalded cat" if you pour enough money on it!
The answer to all the other questions is "yes"! -- If you don't put in "heavier parts" (everywhere), - save the wheelbarrow to carry parts home with when you go out!