when i replced my steel tub with a fiberglass one this last spring, i cut the first four mounts to 3" lengths. this meant i would have a 1" body lift, stock height uses 2" legths. and contrary to the previous post, you are supposed to cut the first 2 sets of mounts the same; meaning the mounts that are right under the firewall, and the next set right under the rear of the door opening. after you have cut and placed these four mounts, place the tub on the frame in the location it will be bolted. then measure the space between the rest of the mounts on the frame and the tub. add approx 1/4" for compression. then cut, squeeze 'em in, and your ready to bolt down. as for clutch linkage... you need not worry to much about a 1" body lift anything more, and adjstments will be necessary. if you have a hydraulic clutch, all the better, because you can then just buy a longer clutch hose, as i did. just watch out for the steering column joints binding.
Good luck. feel free to email me if you have anymore questions. i also have a write up on my website about tub swapping
'83 CJ-7, 258, TR ignition, headers, T5/D300, 3" suspension, 1" body, Moser 1 pce axles, Model 20, 3.54:1