Having a working tach is a low priority at this time. I'm real concerned that the adapter will be a stalling point for this project.

Have you measured the trans input shaft / clutch distances to be sure your adapter will space the trans properly?

Using a cone on the back of the flywheel is an iffy mod. I'd expect it to move around over time. Starting out with a 2.3 / 2.5 Ford FW would be a better possibility.

There is even a chance the stock MB manual trans FW could be modified to take the Ford clutch.

If an off the shelf adapter package exists, buy it.