Thanks for your advice Brian & Gregory,
I’ll look up Eric Lee for advice & will try the Canadian Tire primer you mentioned.
There are several firms that have offered to do the welding on their premises. Since only a few sections need butt welding I’d prefer not to move the car. Ideally the welds should be planished just after welding to blend the two panels together. I’m willing to compensate for someone to do the work in my garage with a portable TIG welder. I’m handy with a MIG welder so the remaining welds aren’t an issue.