Lawnman before you buy a Gheenoe or Riverhawk I would suggest you hitch a ride in either one. I owned a fished from a Gheenoe for a season or more. I found it to be a little small to fish two adults from while standing. I rigged it with a 2005 Mercury 2 stroke prop o/b which I was not happy with for the Caney Fork at low water levels. I converted the Mercury to a jet and ran it on the Gheenoe as well. It worked ok. The narrow transom width and lack of a wide bottom really proved to me that a Gheenoe or Riverhawk is not suited for a jet o/b.
I would look at selling your Jonhson jet, if you're happy with you hull, and buy a Yamaha 40/30 4 stroke o/b jet. I would get one with electric start. Having owned one of these motors and regretting ever selling my jet sled I will someday have another one. Also the Yamaha 40/30 4 stroke sips fuel compared to my Mercury 25/20 2 stroke jet
On the used market I would expect to get $1700 to $2300 for your Johnson jet o/b.
Another ideal might be to buy a light hull more suited for your current jet.
Good Luck,
Glenn