oh sh*t if your looking for 1500hp, well its not gonna happen. just as a reality check, a 1500hp ls1 is 7 second car. So ill give you a realistic goal of about 850-900whp, or a low 9 sec. car. Send off the block and get a built 402 shortblock from SLP or something, or just order the kit and do it that way. For that much power your gonna need the extra cubes, its just waaaay too much easier this way. then order up a set of GMPP new L92 heads and single plane intake manifold. i would suggest finding a junkyard to grab all the little covers and coils etc. off a blown engine. otherwise, get a trashed complete pullout off ebay, should be cheap as hell and will give you all the stuff, and your bottom end to pull it together. those heads flow 330cfm out of the box, and on a 402 will make BIG power. go get this months GM high tech performance magazine if you dont have it. they put these on a stock bottom end LS2 (364ci), with a good sized cam and made 545hp. with a turbo i would say this combo, 402 L92 heads, single plane, and a cam around 236@.050 would support up to 1400hp. i dont see 1000whp being out of the question with around 14psi.
And on the front drivers side of the block, it will be cast with a 6.0, or 5.3. another way to tell is if it has #317 heads its a 6.0, 5.3 and 4.8 had #882 if i remember right.
Gary