Serious misuse of punctuation leaves me wondering what the hell you are trying to say?
225 cases
I guess what I'm trying to say is, you can't use the xt/serow/ttr cases without using the xt/serow/ttr clutch cover. If you mix and match by using a TW clutch cover then you will run into crankcase ventilation problems (although this can be overcome by an experienced builder). So It's best to stick with 5 speed TW transmission + six disk clutch + xt clutch cover.
200 cases(to 225cc upgrade)
Or alternately, switch an XT crank+balancer assembly into a bored out TW200 bottom cases then use the 5 disk clutch.
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The easiest route by far is just to install a tw200 motor in place of the tw125 motor. But..... TW200 motors only came to certain countries, and since the OP said he had a TW125, then he is not from one of those countries, hence the above mix and match solutions. Below is 125 cases mix recipe
125 cases
You'll need a 225cc entire top end, a case bore to 78mm, entire 225 crank assembly, 225 balancer, bearings, flywheel, and a 200cc 5 disk clutch would be highly recommended, you can use the TW125 transmission. It is also possible to use the 200cc top end/crank, but it is the same expense and hassle as the 225 stuff, so why bother.
Note
There is a difference in the 225 cases in the left balancer bearing area that allows a larger bearing, and some ventilation differences. It may be easier to use a 200cc balancer in 200/125 cases because of this, Yamaha used the 200 balancer in "early dirt only" 225 trikes, so it is perfectly OK, but there may be slightly more vibes on the street.