I was about to say in the Husky thread what a good deal you got, maybe not so
It looks clean enough, I got my 87 KX 250 for similar money ( 2 chambers + 1 chamber fix) So far I have found the airbox lid held on with whitworth bolts, need I say more
I assume the cover is magnesium?
The easiest way to fix is to replace but as you say good ones for that model would be hard to find.
It should weld okay so long as their is good base material their some where. The other drama will be any machining required if the pump shaft or seal needs supporting.