Sorry, cannot convert a MIG to stick. MIG are also known as "wirefeed" welders because of the spool.

I have seen a few stick welders with a MIG wirefeed attachment on them. Also, many TIG welders have stick capability so I would guess that there would be a chance of putting a MIG attachment on some of them.

Have never seen a MIG setup that could be converted to stick or TIG though.

I am not especially familiar with the Clark brand other than hearing about it on the forums. I'd say that if you were looking to do anything heavy, then you would be looking at one of the two "commercial" units at the bottom of the page.

That is sort of the thing about taking a class and "trying before you buy." Starting out with even a 115V model and you think you're doing pretty good. Then you have a chance to use a professional model and you realize what all the "hobbiest" version is lacking.