Yeah that oil filter can be a problem. Apparently the earlier W115 617 NA block casting is different where the oil filter housing attaches, so you can't use the earlier canister oil filter on a later W123 617 block. I believe the workaround for a later engine in a W114/W115 is installing an adapter plate with hose fittings to the block and using a remote filter.

The '85 Cali engine is turbo, right?, which opens up another can of worms. I'm pretty sure stock manifold/turbo will not fit under the body brace, and there might be some side clearance issues too due to the relatively narrow space between the frame rails in the W114/W115 engine bay, but I'm guessing about that. I've not done this swap myself hence the "guessing" but have lurked here long enough to have read posts by others who have.

And the flywheel is another thought. Euro W115 300Ds could be had with stick shift, and they came with a heavier flywheel. I saw a thread about one of these cars here not too long ago with pics of that flywheel. I don't think it's necessary to have it, though. I know a guy in Albuquerque who put a 4 speed stick into a W123 NA 300D. He used a flywheel from a 616 and it seems to work fine as the car is regularly driven.

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D