DRounds

I am trying to change engines in my RW713. I have a RW753 parts truck, with 3406Cengine, but want to keep 12 speed from RW713. Seem the rear cab mount/cross member will not clear 12 speed. Thought there were RW753's with 12 speeds manufactured. Have all other engine mounts, front cross member, radiator and piping, just trying to make it work. Will resort to Road Ranger transmission if necessary. Looking for any information. Thanks!!