Zack, yes in my opinion the weld wouldn't cause any heat damage at that distance and after all it is an item designed to get blooooody hot! you could replace the coupling with a stainless version as well. It seems most of the cats are in the 200 class. Check Dave Wellings out , he had a new cat fabricated in the 300 range as he always from new has had difficulty getting under the emissions threshold .
Bit of a typo there? Think standard CATs are 400 cell. The higher the cell count, the greater surface area and hence less emissions
Incidentally, I once had a leaky weld on my CAT, on the smaller end of the conical reduction leading to the incoming exhaust pipe. Had it welded up and it has passed 2 MOT s since.
