Best Way to reach 500 hp ,, Cheap !

I think in order to get more than another 40-50 you will have to do some work on the bottom end too. Crates are notorious for poor machining and assembly. So you will want to make sure that is all "right". Not functional, but perfect. A good way to see how things are is to do a leak down of the engine as it stands. Better heads, higher static compression, perfect ring seal, internal balancing, and a big cam will pretty easily reach 450hp but it will be at higher rpms. The out and out easiest way would be to get a 4" arm and stroke it to 408/410. You'll still need almost everything else new and better anyway, so you can get some money by selling that stuff. That will get you 500/500.