I just use a flat sheet of 15mm thick Aluminium plate on my RIB to use an XL shaft engine.
The transom had been cut for a Long Shaft engine when I brought the boat many years ago, but it just kept getting swamped.
The bottom engine mounting bolts go through the plate and transom, where the bolts are in the images, and the top moiunting bolts just go through the plate.
I've had no issues with this system holding my old DT200EFI on for years, even in some pretty rough weather, and I've just rebuilt it for the 225 Opti I'm installing.
You can really spread the load out across the transom with widely spaced bolts.
All the bolts that can't be seen under the transom cover have 6in diameter 3mm thick Stainless pads behind them.