I am not sure about the LSX's, so can't help you there. But for a normal small block to handle 550RWHP, you need a engine that runs! The first engine in my 69 (for turbos) was a wore out, hone job only .040 over, "Badger" brand (Cheapest I could find) hyper pistons, stock rods (and bolts!!), cast crank, 2 bolt block, small turbo grind cam, JUNK 882 casting heads, Victor Jr intake and Holley 650 with 2 junkyard T-Bird turbos blowing thru a GOOD intercooler into it. Worked GREAT for 2 1/2 years and about 15,000+ miles of me beating on it before the sloppy bore allowed the cheapie pistons to loose the skirts and finally split the cyl wall. The car was still running great (actually at the dragstrip) when it started puking water out the pipes. That combo had 500RWHP with a BAD rich tune (like not even on the wideband!) and was running WAAAAY low 11's in a car that did not work at the track, that day it was going into the 10's for sure. BTW-3.00 gear also!
That combo cost about $4,000 TOTAL! If you want stupid power, that is another story, but just to run mid 10's, it don't take much if your car works at the track. The most important thing is to keep a good tune and keep it out of detonation. Cheap parts will work just fine at that level if it stays clean!

BTW-Good (expensive) parts are generally longer lasting and probably better and more advisable (........and yada, yada, yada......), but I am just saying that they are not absolutely necessary if the funds are not there, you do not have to have a "billet" engine to make it work good