We used the muffler that fit. There isn't a lot of room for a full 3 inch exhaust under an A body car so there were not many choices. In fact, I think once we laid the whole system out there was only one muffler available that actually fit in the space. I considered cutting the floor to provide more space but the fabricator I was working with said he could make it work. The exhaust system did end up costing a pile of money since it took the fab guy two days and a big box of mandrel bends. But it fits and works and is tucked up out of the way which is what I wanted. I'm not a fan of exhaust systems that hang down below the car.