trainguy;
I am going to ask the question regarding specific application because ASTM A710 is not material that is readily welded, like typical structural steels. This material is an age hardening structural steel that requires extreme caution for welding. What is your weld detail between these members? The filler metal selection is easy - a 309 stainless steel.
I would suggest you qualify this material for welding using AWS D1.1 as a guide.