Outer Limits 4x4 Board

Wondering how much trouble you'd have fitting a manual box from 100 series 1hdfte to 80 series 1hz? Basically same gearbox but use different size clutch right?

yep. pretty much. just gotta match flywheel size and input shaft splines to the clutch kit.

So I can get away with using the clutch and fly wheel off the z? Only asking this as I can pick up a good cheap box out of a 100 series.

No, the input shaft is different, I'm in the process of collecting parts to do the same conversion. you either need to use 1HDseries fly wheel and clutch plates, or have someone like exedy clutch make a hybrid clutch plate for you.
Transfer case inputs are different also.