Personally, I don't have a problem with the approximately 1/16" extension the inserts probably add to each of the lower longerons. The reality is that they are attached over a foot and a half from the upper firebox support framing. I doubt a carpenter's square could see much deviation. Interestingly, if you do a search on this topic there is a lot of discussion on the different types of inserts and their effectiveness for steel channel framing repair. I actually really like the look of what you did with the small reveal of the threaded insert plate at the joint. Instead of painting it over, you show the plate and bolt which looks like a functional element. Your uncle is going love that grill.