Update...not so bright...

[Airslot]

Jeff, lets get er done. You got a boat to fish out of, so lets get to work. Since your this far along, I'd just replace the stringers if there is any question.

3/4" plywood, ACX, would be as good a core material as you'll find. Your concern over twisting is very valid. I'm thinking that you could do one stringer at a time without the hull deforming on you. Look into prices at shopmaninc.com for epoxy prices. May as well look at 30 gallons. If you glass in that wood, she'll not rot in your liftime.

Good Luck, we are here as your support group.