The input power is not a problem, I can add a subpanel to the garage. Most of the older transformer machines need around 100A-125A wide open. The extra current would be for aluminum, so the XMT wouldn't work. I was thinking a syncrowave or lincoln squarewave. I also saw an Esab heliarc with a cooler...

How often do you guys need more than 200 amps when you are TIG welding? I haven't run into it yet, but i continue to see screaming deals on older used transformer TIGs that would get me to 310-315A max. Thoughts?

What are you using for the heat exchanger/radiator? I ended up buying my cooler from HTP when i got my TIG, which was around $500. I thought about making my own like you are doing, and i figured it would end up being around $300 or so for the parts. I am curious to see how it works.