Bruce L. Bergman writes:

(lots and lots of good advice snipped)

Either that, or fake up a few test coupons with the same material
in the same configuration, weld them up, and then beat on it hard with
a sledgehammer to proof your design & technique. If the base metal
gives before the welds and only after a lot of abuse, the welds are
good.

Thanks -- this is all extremely helpful!