Mike,
Are you continuing with the recore.
More pics would be great!
Doubt that acetone would break any old frp down. Tho it might loosen things up if there already was some kind of deterioration. For yerself, breath as little of it as possible. If you can smell it, you're breathing it.
That's the reason to stay away from polyester: acetone and styrene.
There has been discussion about using solvents to clean up work. Concensus is that solvents can invade work and lurk in pores and screw up the mechanical bond between plastics. Even extreme volatiles like acetone.
{338 just had a puzzling epoxy to deck failure. I decide to fill in the depressions along the deck outside the coamings. It seemed pretty easy, tho arguably a waste of epoxy. The strip of decks have been sanded and cleaned off and on - the gelcoat anti-skid long gone, subsequent sanding showing a little of the glass in spots. As I do I scoured the hell out of the decks, dedusted by dry wiping and brushed on a coating of plain epoxy, the same laminating (runny) epoxy I always use. Then wiped off any runny stuff, mixed up some silica, milled glass, epoxy into a spreadable gel. I scrubbed in the gel first with a brush, and then bladed on a fairing layer of the goop.
Came back two day later epecting to scuff-sand and apply 407. It somehow didn't look right, so a 1" utility chisel came to hand
and, it took some work, but all it came off as if it was sugar candy. Pieces like broken peanut brittle. The pieces had the 36 grit scoring of the deck reproduced on the underside. NOTHING HAD STUCK. The deck in front and behind had hibuild epoxy primer on it (plenty of gelcoat still on the deck), no problem not sticking that I can see.}
Any ideas?