Paul..
That is a nice weld..low splatter..looks like 7018 or 7011..
7011 would give you a nice base for a deep large weld but not with a frame..but not strong enough for a stand alone,one pass fix,in my estimation..especially for a restoration.... the 7018 is your best choice for price and strength.....70 series means 70,000 pounds tensile strength..more than enough for your frame..if it was a military application I would use 8018 or even 9018 for a 90,000 pound tensile strength weld..the frame would break somewhere else..not the welded area..
Anyway ..by the look of your weld..you don't need any advice from me but it may help others that are doing some welding with out your experience that may have some questions that we could help with..Keep posting..love the pictures and the description..
