Well,
It turns out that since you had a backup, I decided to go ahead and MIG the broken piece and then weld it back on the heat shield. Everything went just right and it is installed back on the Dog and ready to roll to work tomorrow. Absolutely no evidence on the outside that I welded on the inside. I kept the heat high enough to get a good weld but short enough duration to not heat up the chrome. I alternated between each spot, cleaning as I went so I got good penetration.
Thanks for the advice,
Huw
PS I may still purchase the extra heat shield from you if I can figure out something else to buy too just so I have it. Although, years later I will probably forget I have it in the attic!