What year truck, what year engine? Are the motor mounts for the old and new engines the same? If not, you'll likely be in and out a couple times before you're done. Took me twice, in to measure and mark, out to fabricate and install mounts, and then in again. Course, it'd been 40 years since the last time I made a switch like that.
Most of the time, you'd slide the trans back and leave the engine/bell housing as a unit until they're out. Depending on year, sometimes it's easier to leave the trans on the engine/bell until the whole thing is out.
