Looks like you are doing everything correct. You are right about the length, it should be exactly 4" longer. All the spline counts, flywheel dia, clutch, pressure plate, pilot bearing, t/case mounts, speedocable, 4WD indicator light switch, flange diameters and bolt sizes will all be the same, even all 5 forward gears and reverse have the same gear ratios.
The U-Bolt crossmember mount is a good idea that involves almost no fabrication. You might have to slot the four outter most holes (2 on each side) of the crossmember because the frame is wider 4" back from the stock location.
If your truck has a body lift kit, then it will make it much eaiser to get the U-bolts up and around the frame.
And Mike is right, since the G54 uses a forward shift t/case, the shifters will be in nearly the same location as your stock setup.
Make sure you use some GL5 80-90W gear oil when you get it all back together.
Regards,
BigMike
