I apologize as I mis-read and thought for some reason you were removing the cats too.....

Allied makes a great set of resonators (and builds most of the more popular industry's mufflers as well) that come in just about any size, diameter & length (10"" to 38"" IIRR)....they have been around for 30+ years and available nationwide from just about any muffler shop (costs are $40-$60 each- wholesale will be less)...if you have to order, typical 24 delivery.

Definitely have to play with the system a bit to get the sound....IMHO- I would look at 28"-30" lengths for the resonators. I have duel 26" inchers on mine....and if I could, I would measure very close to see if I could properly fit the longest I could get in there.