Looks like you are making good progress. I am kind of in the same boat. I have a '65 C10 that needs a portion of the passenger floor pan, kick panel and rocker arm replaced. At this time I'm cutting out the rust.
I plan to purchase a MIG and learn how to use it just as you are doing. Therefore can you pls. elaborate on your welding setup? Did you already have a MIG? What brand/model are you using? You mentioned the new wire made a difference. What kind and diameter was the old wire and new?
