I'm putting the final touches on a project for school and I figured that I would do a little survey before I submit it. Now I know something like this wouldn't be cheap but it's completely hypothetical so bare with me before everyone starts shouting about the complexity and dealing with modern computers....
Basically it would be a service that offers engine upgrades for older Mercedes-Benz and Land Rovers. Restoration would also be offered of course and later on I think it would be nice to master interior upgrades (Reupholstering the original seats with new colors and stiching leather to the dashboards for a nice modern touch)
The Mercedes-Benz, namely the 80's models, would receive more modern engines a la Roncallos M120 R107 project (Ok credit wheres it's due, that was part of the inspiration for the entire project...also the teacher said we should stick with what we know

) I think the M120 would be a good place to start but I think the M113 would be a really good paring for a W126/R107.
That Land Rovers would ditch their crappy Rover V8s for Mercedes diesels (Yes it has been done!) Series Rovers would be a good place to start with OM617s but the volume really isn't all there. So the original Discovery and Range Rover Classics would probably be a better cornerstone once its figured out how to get a 603 or 606 into one of them.