Neat shifter, I like it! Don't distress over the tig vs. mig deal. Any prototype is about function first - right? Judging visually that weld is an inert gas weld with like .045 wire and it is w-e-l-d-e-d. Maybe try this, use a little .035 or smaller flux-cored wire and take the gas nozzle off your mig gun. This will allow a bit more precision as the nozzle is gone and the contact tip is all you have to deal with. The contact tip is electrically hot but it is easy enough to keep it off the work or you could just insulate it. Don't try a continuos weld... just a quick puddle then release and do it again. Kind of like spot welding but the object is to do a series of circular spots each of which covers the last about 40-50%. Done quickly the puddle never cools enough to prevent admix of the filler with the previous dot of weld. You'll get the hang of it quickly and produce welds that rival the appearance of any tig weld - will kinda look like a stack of tiny dimes wrapped around the flange of your shifter. I own 3 tig machines and I am well aware of the public mystique with tig processes... sure tig works great on al, ss, c-moly etc. but mig does too and is way faster and certainly the standard of production now; after all, tig is little more than an electric torch! If you want to stay with a continuous gas weld build a spindle fixture to turn the piece on and have a buddy turn the whole thing while you stay in place and weld - or a fixture to hold the gun while you pull the trigger and turn the work. Just my long-winded two-cents worth...