You can roll or brush epoxy primer. Use 2 coats. It sands and feathers quite well in my experience.
I would highly recommend epoxy primer over a welded area. Too many irregularities in final metal thickness and possible undetectable pin holes to risk using other primers.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission