I can't help but would love to see this in action.
I was helping a weld shop with welding procedures for square groove joints where 3/8" plate was butted together and welded for large transformer shells. Lincoln Electric's local rep brought a FCAW Bug-O track machine by and we were able to get acceptable results in one pass from one side.
But you are trying 1" to 1.25" joints...that is a lot of energy being focused into the joint to weld that much material.