A 24 inch muffler would have to hang entirely below the chassis outriggers. My mufflers suck up between the outriggers in the pocket they form. Only the 2-1/2 inch pipes have to clear the outriggers. (See Bob's note above about the pocket measuring 19.25 inch). So I'm not sure I understand what Doug is saying about a 24 inch muffler fitting.
That would put the mufflers about 1-1/4 inches lower than my mufflers at least. That is going to be hanging down pretty low.