318 v 360

Why do you need 450hp? (See above post about what your priorities need to be.) If you have very limited funds, leave the 318 as is for now. replace the rear w 8 3/4 and something like 3.55s or 3.23s and add a shift kit. Then get a decent dual exh system on it. Preferably with headers. When those are done, then think about a bigger engine. or more power.