Fabricated the engine mount this morning out of 6mmx6mm hardwood and 4mm ply. Cut some slots on the sides and the mount is a nice snug fit. I have glued it in place with thin CA and will give it a bit of coating with epoxy later this day, along with gluing the bottom piece of ply thats serves s bracing.
Seems like the MiniMag was made for the small OS!