This should work really well. There are a couple of things you'll want to consider/remember if you bond the cabinets to the shell.
The first is that a bond is only as strong as the stuff you're bonding to. If you simply bond the cabinet flange to the shell with epoxy, all the epoxy has to bond to is the polyester resin on the topmost surfaces of the fiberglass, and that's probably quite sufficient as long as the whole cabinet flange has an epoxy bond to the shell and not just a thin line where the two surfaces come into contact.
My suggestion: make a 50/50 paste of 60 minute epoxy and glass "microspheres," available at most plastics places that sell fiberglassing supplies, and apply a thick layer paste to the cabinet flange before (temporarily) securing it into the hull using the old screw holes. Doing it this way will squish the epoxy paste into the uneven surfaces. You can clean up the edges where the epoxy mix squishes out using denatured alcohol, which can also be used to thin the paste if you wind up making it a bit too thick.
Epoxy-microsphere paste makes for a very strong & lightweight adhesive, but be careful to wear a quality NIOSH dust mask when handling dry microspheres. Microspheres loft into the air very readily and are a respiratory hazard. Disposable gloves and goggles are a good idea, too, as the microspheres will coat your skin and break into a fine glass dust that can make you itch.
Whatever method you do use to bond the two surfaces together, make sure they come into good contact and the bonding material can transmit heat from the shell to the cabinet so they both expand and contract at the same rate, otherwise either the adhesive or the surfaces of the shell and cabinet will crack and the bond will fail.
Another thought on and alternative to directly bonding the cabinets to the shell: you might consider epoxying carriage bolts into 2" square punched metal sheets and fiberglass those to the shell where the old rivet holes are. That would allow you to use the same Reflectix/Rat Fur insulation treatment modern Scamps use and you'd still be able to remove the cabinets if you wanted to paint
or replace them.