Not trying to stir the pot – this is just my experience.
I priced it out and IIRC you can replace almost every wear item with new for about $650. Head, block, everything. Just keep the intake, exhaust, ignition and exterior bits and the rest is basically new. A motor that’s not in that bad of shape might not need much more than Alan describes. For a play motor, it’s hard to understand why it matters if it’s new or not.
Spent $750 to have my block align-bored to first over and put a new head on mine. Ran great afterwards and that’s a lot cheaper than a grand but I didn’t get a box of good spares from the deal. <shrug> Dono.