Hi Paul,
500 hp from a 400 is possible with out a stroker kit, but it would require ported aluminum heads that flow over 300 cfm, 93 octane, and a serious tune- this combo would also haved to be revved to 5000-5500, not a big deal but a bit much on a regular basis for a Pontiac V-8. This output is alot easier coming from a 400/461 stroker combo- it can make 500 hp from stock e-heads or KRE's and do this at least 1000 rpm lower, saving wear and tear on the engine.
A 70-75 no.481988 400 block is the best candidate for your build- it has 5 mounting holes per side and will drop into your 79 Bird w/o adapter brackets. 4-bolt caps are nice, but even a 2-bolt 400 block can support 600 hp- stock bolts will work, but ARP main studs are preferred for performance builds.
I get most of major parts like pistons, rings, rods, bearings, cams, etc. for my builds from Pacific Performance Racing. Ken 'Ace' Brewer has been building high-performance Ponchos for over 24+ years and is one of the most knowledgeable builders I know. He can guide you in the right direction in putting together your parts list for your build, and has all the parts you need to build a nice performance Pontiac V-8.
Geno