I can't help you on the suspension travel, but on the engine the 300E engine will come closer to fit, but the starter provision in the bell housing will be on the opposite side of the 421 tranny. you will probably need to machine an adapter to mount it, or you could find an OM617A 5cyl turbo diesel engine, it will bolt up to the tranny and can use the flywheel from the 421 engine if you have it rebalanced. If you want to go gas you could put in a M110 2.8 dohc 6cyl out of a 280SE sedan and it will bolt to the trans, but you will need to find a 280GE G wagen flywheel and clutch to make it work.
Hope this helps.
Cheers,
Ben
Hope this helps.
Cheers,
Ben