Cruiser,
air flow equals power. the best bang for the buck would be exhaust, intake manifold, HEI style distributor, cam, heads and then compression ratio. this is assuming that your lower end is in good shape. if you decide to rebuild the lower end and up the compression, you can get away with 10.5 to 1 if and ONLY IF you run aluminum heads. Dynomax makes a good header/dual-pipe/ultraflow muffler combo that fits and performs well, about $600 for the system. intake manifolds are about $200, as well as distributors with tuning kits. and heads run from $500/pr for iron, up to $1800 for nice race alumies. if you are going for a nice 350/350, you can run just about any head out there, but if you want 500hp you need to run AFR or at least Brodix along with a new lower end. i would not do a head upgrade, unless the lower end is at least 95% perfect, you will be wasting time and cash.
i would run a Weiand dual plane intake, Dynomax exhaust system, maybe a cam change, and a MSD distributor with your Q-jet. pricing shoud be around $1200 for everything and the difference will be noticable. have fun tinkering, Brian