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.

Thanks mark! Do you know if the internals of the DT engine fit the IT case? Like crankshaft, gearbox and clutch? Seems a little complicated to find IT cases and much easier to find another DT175MX engine.

Without reading it all yet--wasn't there an mx175 semi racer. Not to be confused with a dt175mx which I thought was only basically an ordinary dt175 nothing go fast!!. So is an mx175 more advanced in porting & would the cylinder with high comp head fit your dt175. Might have to lengthen the header or center of the chamber exhaust to bring the power down lower in the revs but still have bulk power & more usable. Then again if parts aren't interchangeable umm ignore me lol. I've seen some pretty crazy go fast 175's on Facebook in Asia I think. Just crazy high horsepower stuff like a full blown race motor on the street.

"Thanks mark! Do you know if the internals of the DT engine fit the IT case? Like crankshaft, gearbox and clutch? Seems a little complicated to find IT cases and much easier to find another DT175MX engine." 

If you're not finding or going to use IT175 cases, why does it matter?  

Most of the "DT" engines are based on the corresponding competition engine architecture.  The 78-81 DT175 monoshock engine is a detuned 77-79 IT175 engine.  

There are some differences like the IT doesn't have an oil pump, tach drive, or neutral light switch (and transmission gear ratios are different).  But it's not nearly as hard or expensive to convert IT cases to match the DT features as it is to modify DT cases to fit the IT cylinder.  (Or you can simply run a complete 77-79 IT175 engine in the DT frame without the oil pump, tach, or neutral switch features)

"If you're not finding or going to use IT175 cases, why does it matter?"

Because I would take this into consideration what to decide for... and I am just curious 
I would like to keep the oil pump, for enduro tours and daily driving I find this really convenient. 
So at the moment it seems to me the easier option to find another complete DT engine for the conversion and put the one I am running right now into the shelf as a spare engine. Anyway... this will be a project for upcoming winter. So still have some time so lets see what I can find first... IT engine, case only, or DT engine