Sorry about the rear ending. That sucks!
Any muffler shop can weld in the bung for you, but my choice of muffler shop is Gene's Muffler's in Downey. They are the only muffler shop in the area that I know that as a mandrel bender. They made my custom X-pipe and also welded in my O2 bung too.
I'm quite curious how that AVS2 will work out for you. I think those have annular boosters right? Kinda interesting. Be sure to post back your results with that carb. The only "dicking" around you might to do is change out the rods, but that's easy and you don't even have to remove the carb for that.
I have a Google sheets calculator that I can share with you that can help you sort of guide your way through to choosing the right rod combination once you know your Air/Fuel ratio.
Where exactly did you take that picture? Nice!! Nice car too. Let's go there for a photo shoot. I'll take my Duster. I need to take new pictures since I have new wheels and tires on it.