Don't bother with 3ks, you can get those virtually free with a couple of washers if you don't have the money for 4ks and valve springs right away. Even with a 5spd free pump mods will be enough to fry a stock clutch. So no matter what you have there is money that will be spent on HOLDING the power.
Start with the following
Mack rack plug
pull the plate (but don't toss it, keep it in your tool box)
Mod your AFC
set your timing at at least 18*
4k gov springs and HD valve springs, or poor man's GSK
GUAGES
pusher pump - I recommend a Carter 4601
External fuel pressure regulator set to around 40psi - cheapo ebay works just fine on the return line
BLACK FUEL PRESSURE REGULATOR ADJUSTABLE 1 TO 140 PSI: eBay Motors (item 270620962896 end time Oct-10-10 14:53:14 PDT)
That would get you pretty close to the 400hp mark on a stock turbo...
If you're not quite happy you could add these next
Head studs
DVs - do NOT install full cuts, I know they're cheap, but they have terrible street manners and run HOT
Injectors - I recommend trying a 7x.010, but good ol' 5x.014s work too
64/71/12 or a HE351VE if you are on a budget - search VGT here there's lots or reading on the 351
If you go with the 351 you'll probably have to cut your plate to a 0 and play with it to take some of the fuel out since the DVs and injectors will really open things up.
That should be good for almost 600hp with the 64, and north of 500 with the 351. Anything more will require some finesse with the pump, or to flat out have a shop build you one and a set of twins to keep up.