The stamp looks real.... engine appears to need a rebuild prior to use, but to be certain you need to disassemble and take to a machine shop to have it thorughly checked. In the current assembled state you can check if std bore or *larger*, and you can check the cylinder ridge to see how worn it is in the cylinders. Generally you should probably consider it to need a minimal boring, and you'll be very lucky if you don't. that means new pistons, and I also align bore (when it's an unknown engine), and check the crank journals. Up to 10 thousandths doesn't bother me either...
(make sure if they do a clean up on the deck, that they stop short of the stamp pad; that stamp looks great so you wouldn't want to disturb it)..
Gary