I'll stick my $0.02 in on the welding question.
As I understand it, M35 frames are mild steel, not spring or hardened steel. Grundletaube informed me that the bumperettes are spring steel. Therefore avoid welding those. Judicious welding on a frame should be fine. The key word is Judicious. 9 times out of 10 it is better to drill & bolt to a frame. Some exceptions that rock crawlers use is to weld reinforcements to their spring hangers. Professional chop shops MIG weld frames all the time when stretching or shortening a custom vehicle.
That welder really needs to clean the metal better first! I mean jeez. Also, ever heard of grinding + multiple passes? I'm sorry but I'd consider that weld you posted as just a filler. Another pass on the top,bottom, then middle would be much stronger. But then you have to start thinking about the heat.
Anyone ever tried TIG? It takes a lot longer. You need to be an octopus on a unicycle to run a bead. But when you are done you have the highest quality, strongest, and smallest heat zone welds. X-ray quality welds on nuclear reactors are TIG. You could run a few inches at a time & have a very strong, clean weld in short order. With TIG you can even weld different metals together. If time is not a concern, then TIG should be your weld of choice. And YES, you can TIG weld just about any steel you can think of with very good results. It's not just for aluminum. The key to any welding job is to clean, clean, then clean again before you even start.