Shouldn't be too hard to find turbo parts for those Mannheim engines... They're pretty common in combine applications, not sure which ones right off the top of my head. But they have some pretty nice after cooled set-ups that are good for 325hp (stock) in some of the big combines. Of course those are a little more than just manifolds and turbo, they've got oil jets to cool the pistons, looser tolerances to allow more expansion and a completely different injection pump. But with what's commonly available you should be able to get 150hp or better before worrying about anything else, the drive train is pretty resilient in those tractors. I would just find a local bone yard and ask for manifolds/turbo from like say a 3155 American... That should get a nice 3LM Schwitzer and everything else you need.