best rust converter?

I have a 74 Duster factory 318/904/8.25
The motor was seized when I bought it and the trans housing had a nasty split in the side.

So for the most part I am left with a rusty roller.

Since I am going to strip the car to the unibody and rebuild it, After I strip it and wire brush the unibody, what is the best rust converter to use before epoxy primer?

Also wondering if an economy wire feed mig welder will be good for welding in patch panels?