Did anybody try to fit the swing arm from a 1978 YZ125 into the DT frame before? I got the chance to buy a complete YZ125 in parts for cheap. I am already pretty sure the fork will fit. The combination of both would be a very nice suspension upgrade! Also I can get a cylinder from the IT175 from the same guy. It's from the model 77-79 and will definitely fit the DT engine. The ports look really promising! But I would also need to upgrade the intake side... 34mm carburetor, intake manifold with boost bottle port, reed valves, find a solution for the airbox... open air filter is not an option as I want to take the bike out in the dirt.

1978 YZ125 swingarm geometry is different.  Rear shock is too big to fit DT frame.  Front forks will not fit.

1977-79 IT175 cylinder definitely will NOT fit DT cases without fairly extensive welding and machine work done to cases.

You're right, I took measurements today of the bottom of both cylinders. IT175 cylinder base is 10mm wider than DT175MX. So I will need to find a spare engine and find somebody who can weld it for me. Really wanna see that IT175 cylinder on my DT! 

About the YZ125 in parts: I bought it and I think I'd rather build a complete bike out of it again. Everything should be there. Lets see when this projects finds a start.

You could also use 77-79 IT175 cases if you can find a good set.  It's a lot less work and much cheaper that way.