Just a quick question.....are the cylinders across the DT400 range (twin shock to monoshock) identical and are there any markings or identification on the cylinders to distinguish them? I think DT400 only produced for 4 years, 2 years twinshock and 2 years monoshock.

Kinda found my answer by using SEARCH....its a wonderful tool..
Seems DT400 twinshock and monoshock model cylinders are not interchangeable....

Still need to know how to distinguish between the 2?

That's good to know. I would have thought they'd all be the same so far as swapping over goes.

There may well be code(s) stamped on them, probably towards the bottom. You might have to rub away some grime first!

Here are a couple of pictures of twinshock 75/76 DT400 USA model cylinders.

They will swap. Someone here has done it. Reed valve flange is different size on the monoshock so that would need to be swapped...

And then you might have trouble finding an intake manifold that lines up if using stock carb/airbox or could work just fine with the earlier/later manifold that matches cylinder flange?

500 being the model code for the 1975 DT400, not the size of the engine!!

The main difference is in the reed cage mount. Its slightly taller on the dual shock models. The intake port on the older models is different as well.

Using an earlier model cylinder on a monoshock bike is possible, but not ideal. You have to use the older reed cage and intake manifold. By doing that your carburetor goes off in a different direction. That causes the top of the carburetor plunger to interfere with the exhaust crossover. Angleing the carb works to remedy this but you still are not able to use the stock intake box. I just use an uni pod filter and bigger main jet.

Thanks for posting confirmation that it "basically" fits and describing the intake/carb/air box differences and alignment issues.