There are 2.5"-3" adaptor
like this that you can weld on or attach with band clamps similar to the OEM clamps between the axle pipe and mid pipe, but the problem will be space, as the axle pipes are the exact length needed to go between the mufflers and the mid pipe. If you're having a muffler shop install it anyhow, they should probably just be able to cut off the appropriate amount from the axle pipes then weld or clamp on a 2.5"-3" adaptor.