Just some stuff to think about...
The "F" body cars, Firebird & Camaro are basically the same cars from 1970 to 1981 with a few minor styling and suspension changes.
The 1970 to '81 "F" bodies do not have "shock towers" to weld up or add braces to. The upper shock mounts are on the sub-frame not the body.
A set of sub-frame connectors will help with the extra torque and the stock rear will probably need some work if you want to put down the torque of the 455. A good set of gears and an Auburn posi unit would work well as would a set of CalTrac traction bars.
A Pontiac 455 and a Chevy 454 are NOT the same motors, not even close. Your 301 is a Pontiac based engine and is the same basic block as the PONTIAC 455. A 455 will bolt in on those mounts. All Pontiac motors are the same basic block configuration from the 301, 326, 350, 389, 400, 421, 428 & 455. Internals are different from size to size and year to year but a little judicious research will give you some insight.
Here is some info... There is a ton of this stuff on the internet. Do some searches...
http://www.carcraft.com/techarticles...ine/index.html
http://www.yearone.com/updatedsingle...ontengid1.html
http://www.krepower.com/