Largest size muffler under an A body?

I know this is 2.5 in and out, but I have 2. I tried one on my 64 slant 6 Valiant and it fit.....barely. It would have fit better had I taken it in to a muffler shop and let them make a different intermediate pipe that would help locate it further up into the muffler area, but all I had was straight pipe and it hung too low, so I put the smaller one back on. It made a nice difference in the sound though. Not that's it's too loud now, I was just curious. I bet the later A bodies might have a little more room, so a good muffler shop could probably make them fit. This is them.

https://www.summitracing.com/parts/wlk-17236