I've done SFCs before. Mostly TIG, sometimes a combination of TIG and stick (big gaps).

I'd like to MIG in a set. Assuming all the welding will be done upside down, and the floor boards / existing frame are 16 gauge steel, the mounting plates are 3/16.

In the past we would grind down the 3/16 to about a 1/16 edge (about a 45-60 bevel) and spot weld all the way around (mostly to keep things from burning down).

Its more or less an upside down lap weld, with a thin piece on top and a thicker piece on the bottom.

Can someone give me an idea what gun angle to try and heat settings.

I'm guessing I setup for the thinner piece and just wet in the thick stuff, but I'm worried about it going down cold. If I setup for the thick stuff and start the weld on the edge of the 3/16 plate, I run the risk of the weld dropping out and not even touching the floor boards.

So questions:
1) Set the heat for 3/16, or the 16 gauge or somewhere inbetween.

2) Gun angle?

3) Start the wire on the 3/16, the 16 gauge, or right at the gap?

4) How long of a bead can I run? 2", 1" before it needs to cool.

Last question,

Has anyone tried the pre-welded SFCs from Global West. I've installed them in the past but welded them completely myself. If the fit is tight, I don't mind paying extra to be that much farther along.
Part 929C is what I'm interested in.

Thanks in advance.

BTW, "screw it and TIG it" is a valid response - just sometimes the gaps are large enough that TIG doesn't seem reasonable.