Interesting concept, putting them back there like that. The consistent bit of advice I've gotten from every muffler manufacturer I've chatted with is that the biggest body I can fit as far upstream in the exhaust the quieter it will be. Based on that, my intent is to fit one of those Kooks or Borla mufflers right after the exit of the downpipe. If those ultra quiet resonators fit back there, an extra 1/2" on each side seems like it aughta reasonably fit further up in the area below the shifter where the tunnel is wider.
It's freaking snowing here again, so I'm delayed, but I need to measure more to confirm or disconfirm the theory.