Grubby John the price is fine. The seller seams to have told you the truth about the build and the sleeve in the cylinder. If KCR built the motor, it should have been tested and setup to specs. There is nothing wrong with a 452 motor if it does have a 428 crank in it. Buy the thing, send it to a machine shop, have it gone through. If it falls the checkout put it back together and get your money back. You may have to go through court system. My only concern is the one sleeve in the block and what happened
Was this a boat motor? I wouldn't rev this thing to 6,500 rpms either. Would make sure it has a HVHP
oil pump and #80 psi spring and min 6 quart
oil pan with 1 extra quart for running.
Rick L.