I have a 4X4 GMT 400 truck that I’d like to Cummins swap. Does the installation of your motor mounts require modifying my frame?

Yes. There is an offset (raised) area at the bottom of both motor mount saddles that need to be trimmed off. The included 3/8″ plates are intended to act as a reinforcement to the pedestals. Preferably, these plates are welded in place, but they can be bolted between the top of the pedestal, and the bottom of the lower motor mount. You’ll also need to install countersunk bolts in the 3 uppermost differential case bolt holes. Some trimming of the differential case webbing is required as well.