So after several iterations and failures (dolly which bent getting stuck in the sand, extension tongue - 2 hitches/balls - was too loose and fell over - and I didn't want a swing out one or permanent one, temporary extension ramp to my trailer - to much stress on the boat/trailer and a pain to crank up....)
I found the dutton-lainson spare-n-dolly attachment. So it's not a swing down but is a spinning bracket for the spare that will go down several inches below the trailer tongue (and a little further behind the jockey wheel). I will add a nice 10 or 12" tire - 4" wide spare. Should be able to just strap to my car and trailer on the hitch bar and pull it up fully loaded with the jockey wheel stowed.
So you get the gold star if it works, which it should...And no new large pieces to add/connect. The dumbest thing I did was not going to the root cause of the issue - the boat slipping off because I didn't have side guide rails on the uneven terrain. A jon boat needs that with the flat bottom....Duh. Added 4 ft side guides now so this should work well....Fingers crossed.