welding these pieces, I've been able to have s junk main case handy so I bolted the clutch case to it, do what you can to clamp it on something flat. If the cover has had a previous ding in it then it'll be twisted to start with.
Don't try to clamp the ring down to the work bench etc. The heat from the welding will distort the case. If you need to hold it to get it tacked on then do it with a c-clamp or something that won't follow the case like a visegrip etc or it'll keep compressing until the case cools down.
I bake the case on a hotplate until I can tap out the governor bearing, not so that the bearing turns blue. The case should sweat out what oil it has absorbed and be much cleaner welding.
Start near the governor area, its the thinnest so do it before it gets too hot to work with. move counter clockwise so you end up at the heaviest portion of the case last.
should go smooth.