Shortblock Upgrade

I bought an assembled, stock, 30 over shortblock and later decided I wanted to upgrade to forged pistons and replace the center main caps with billit ones. Is this hard to do after the fact? I heard it could be but I can only see gapping some new rings, possibly checking for the allignment of the two new caps, and new main bearings. I'm no machinist obviously so I wanted your guys thoughts. Thanks for the help!

P.S. I've already got the pistons and billit caps picked out and priced. I just want to know what I can expect to pay for extra.