We went the route of least resistance and purchased a Sony CDX-GT66UPW:
Sony CDX-GT66UPW Flip-Down CD Receiver - Walmart.com
It is an exact match for the existing wiring and plug...just plugged it in to the harness and it fired right up. No fuss, no muss. It sounds fine and has some of the new bells and whistles but not all of them. It has a USB input which we might use. We weren't that likely to use most of the new stuff anyway.
As long as it keeps working we're happy campers. Now back to getting the leak from the solar panel cables plugged, the fiberglass repaired and the replacement solar panel bolted on. Expecting the kit and stuff to arrive in the next few days.
Thanks for the input!