I dont understand how a crate engine could have worn valve guides?
I see a lot of crate engines come with all brand new parts,including blocks. I understand some are better than others. I also understand price counts too.(no free lunch) My friend John Graham purchased a crate 540 race engine and it came to his shop exactly as advertised.He races in Calgary and is a well know 9.90 racer.
Maybe the economy engines are more of a problem? I tell people that a stock engine is not that much cheaper than high performance. A new cam is the same price if its small or large,new springs are the same price,etc,,, a square block is the same price for stock as race. I expect a g note on machining and I balance all but the cheapest engines.