Hey folks, just to let you know, I did build one. It's based on this design,
On-Board Welder. I have mine on an old pressure washer frame, with an 8 hp B&S engine with electric start. I had to have a battery on it anyway, so it was easy to incorporate. I found a 100 amp alternator at Pull-a-part in Nashville for the basis of my welder. I worked very well with 3/32 rods, and you can hook 'em up to run straight or reverse polarity. Mine isn't running now, as the float stuck open, and filled the crankcase with gas, and the next time I started it, ugh.