Arghhhhh. Crap.
The MC-58 serial number range starts at 6,000 . Some believe this is where the military M65 production ended and the higher # M65s went to the DSC for shipment to where ever they were needed ( me included ) . Others believe that some higher #s are USMC issue , too .
Doesn't matter in this case. Your M65 was indeed a USMC WW2 trainer . Pox on the stamper and the horse he rode in on.
Chris