Slant Six Build help needed

Welcome...It really depends on how much $$ you want spend and how far you want to tear into the internals. Better performance on a budget could be as simple as exhaust, and a 3.55 or 3.91 gear set. A Holley 390 would also be a better choice as you'll be over carbureted with the 650 unless your engine is highly modified. Also, a stock fuel pump is more than adequate for most engine builds...no need to go electric.
The /6 is no V8 and has limitations when it comes to making power...but with that being said, it's a bullet proof engine that can make respectable power when done right. Keep it simple, take your build one step at a time, and evaluate the results of your mods...you might find that a few simple mods go a long way.