You can't install the engine first. That cutout and the inner transom shield that attaches to the gimbal housing is what the the rear motor mounts.
You do realize the transom has some very tight specs on thickness, flatness, and parallelism, along with specific locations of the X dimension (that is the center-line of the crankshaft) don't you?
Thks for the response Don S , I just needed to confirm that , We did do a transom cutout in M M school 10 years ago. my memory is the thing i miss the most! could try to find the books but this was easier...... thks for the link if i decide to do it myself ..Leo