Hello from Roseville Ca.
Im splitting the case on a 78 IT400.
question is, which half comes off first, clutch or the flywheel side.

thanks is advance. 

hello to everyone, been awhile since last post. 

Just talking generally, the right side main bearing is theoreticaly a slide fit on the shaft & retained by the gear & nut.
Of course they hang on a bit if not been off for 'ever' but if you undo everything that's likely to interfere with the case coming off it 'should' lift off with a bit of a plastic or copper/hyde hammer tap on the crank.
Take the detent plunger out of the drum cam end underneath incase the drum gets dragged off the plunger then sit back against it.
Check the drum end can't get caught on the way out of the right case--as case comes off over it.
Things like that. I'm guessing without looking but i'm familiar with that type even if it was 50 years ago lol. [can't remember yesterday though].
Had one of those motors in a "78 DT250 [not on the road though]--was fun!!.