I've seen bolts come out of the pressure plate / coil spring escape and get caught between the flywheel and bell housing.

If you were going to convert to an auto, I'd probably go with a 4 speed GM 700R4 with lockup torque converter.

Given MB diesel engines are a popular conversion into US domestic cars / trucks, there are a few adapter kits floating around but you would need to verify what you have. And of course, the best bet is to find another bell housing and fix what you have.