What are they selling for 6-900? I know the gasket kits alone are over $500

I have yet to hear about anyone having trouble with cheap gaskets or parts, but I'd still try to find a kit with Mr. Gasket/ Felpro stuff. Rock auto has some federal mogul pistons, IIRC they have the 4.005 or 4.010, but they're $$

I don't know if this helps, but my buddy got LS2 dropouts/rods for his and bored it .065, which was still less than new pistons