About 52"? Or was it 63"...? I did this not long ago but I don't remember the maximum space available. I ended up with an 18" and 22". It was perfect with just the 18" when I had cats. But I needed that extra 22" to quiet it after losing them for the headers. It's not obtrusively loud at all now.
From the crossmember after the third cat, back to the exhaust hangers in front of the axle, 40".
Since I have the three and a half inch stainless works exhaust on there, they have a little bend to go from the y-pipe and move it over a little so you can run a center inlet center outlet muffler.
From the end of that bend to the exhaust hanger is about 30"
The first thing I did to this exhaust was cut off the resonator on the stock system because it was hideous hanging underneath the back there behind the rear tire. So I really don't want to put anything on that section of exhaust again if I don't have to but we will see what I figure out... Turns out 3.5 in piping isn't as common as three or four... Not as many options as I was hoping for. Looking at some Walker quiet flow stuff, or maybe even a combination of different style flowmasters... A little disappointed in not finding what I want in the sizes I would like.
The two different mufflers I've tried after getting rid of the factory one, have both had drone to some degree and I really want to avoid that. However the factory muffler with no resonator didn't sound any different to me in the car.
I had a set of flowmaster dbx mufflers on my subaru, and I have one on my little 1.8 l Chevy LUV and on the Subaru they were barely noticeably louder than stock and had zero rasp and sounded decent. And on my little truck almost the same deal. Very quiet and zero rasp.
So I was trying to find one of those to use as a resonator if nothing else, but I would have to go up to a 4-in and when I do that it's a 20 inch long muffler so that doesn't leave much room for something else in there.