Parts that have been assembled but not run can be mixed and matched with no problem. Only things like gaskets that wont seal after being crushed need to be replaced. But saying that I have reused gaskets that were crushed but not run with no problems. After its been run any disassembled parts should stay matched to their locations because of slight tolerance differences.

500hp?? What are you using for rod bolts? Thats the only thing I wouldnt reuse after torquing.

-SP