I'm using a Bisson 09661 Pitts Muffler for the ZDZ 60 -- it bolts right up (44 mm bolt spacing I think) and doesn't leak. The exhaust port doesn't exactly match the muffler as it is a flattened oval shape, not rectangular as shown in the dimensional drawing. Performance doesn't seem to suffer though, as I'm getting about 7,100 rpm on the ground using a Bolly carbon 22-8. Best price for the muffler I've found is at Chief Aircraft.

If you decide to go the MVVS route, I have some additional suggestions for muffler installation that will help you in the long run. I don't have any cowl off photos handy, but would gladly provide them if needed.