I didn't realize before that those were two different Futuras. I wonder why Glastron would have done that. That big chunk of plywood mounted to the outside of the hull and anchoring the engine and outdrive at the top of the transom???
That plywood is inside the boat, the outside is the outer shell of the fiberglass hull.
Don't all IOs have stringers for motor mounts?
Not all of them did. Mercury's Mercruiser 60-90 horse power I/O's using a Renault in-line 4 cylinder engine in the later 60's into the early 70's was bolted to the transom, the front of the engine floated. I think some of the early Volvo Penta 4 cylinder engines were also floaters. Mercruiser 110/120, 140, and in-line 6 GM engines had a single mount at the front of the engine that bolted to a horizontal plank which was glassed between the two main stringers, the rear of the engine was supported by the transom assembly which is bolted thru the transom.
Maybe Mercury made those brackets so they'd vibrate like a MerCruiser.
I'm pretty sure that mounting bracket is OMC manufacture. The engine is supposed to have some movement independent of the hull/transom, so it's got rubber shock bushings.