I have to say i think the only way to build an engine is start from scratch. So often people will rebore and new pistons just to knock the big ends out, they do the big ends and it takes the mains out. Bores that look good are often not round. Pistons cold are never round anyway
Valves are matched to their guides but would you fit old valves and guides and would you not re cut the seats anyway ? More power is more thrust on the thrust bearings and so on and so on....and what about balancing ?
I realise all this is expense but you are looking at not just a stock engine, you are looking at getting a couple of hundred extra bhp out of it as well ?
Obviously i work in the bike engine world and all these things are much more manageable, separate barrels and parts you can actually pick up for starters but surely principles the same ...