Too bad you weren't in Savannah, I could have probably helped you out. I Tig weld stainless aircraft exhaust quite often and have the proper rods (347) for 321 stainless tube.
Last week I just finished up replacing 4 tubes in a Lancair 235 engine mount that had a nose gear failure.
And we are steady working on the 4P we are finishing in the shop.........
Good luck,
Swaid