Build me a Small block
Question is how long do you want your 500 HP to last? Stock rebuilt 360 with good pistons (Hypers will do for now), nothin' fancy cam cam ( like Comp XE285XL),fresh j heads, used intake of some sort ($75 Torker) and $500 Nitrous kit (NOS or Zex or whoever)will get you there for cheap but who knows how long it will last. Ever watch Pinks? Or build it to last with forged-everything stroker stuff, modified Eddies, etc. and hang on to it for awhile. Motors are kinda like some woman I know. Cheap and fast or costly but good for the long run.