You'll run into a couple of issues trying to play Punch-Out in a single monitor JAMMA cabinet. When I made a JAMMA adaptor for PO, I had the advantage that the cabinet wired for JAMMA was an actual PO cabinet that had been converted to JAMMA wiring before I got it, but it still had both Nintendo/Sanyo monitors and both sound amps which are mounted to those monitors. I only did it as an interim solution until I could find a real PO wiring harness, which I found about a month later.
The issues you will have are:
1. With only one monitor, while you can play the game, you won't be able to see your score, time limit or the health meters for yourself or your opponent.
2. Unless you have a Nintendo monitor in your JAMMA cabinet, you would have to rig something up to get sound, because the Punch-Out boardset has no integrated amp. Even if you have a Nintendo monitor in your cabinet, you would still need to make a custom shielded audio cable with a connector that will interface with the Nintendo/Sanyo sound amp.