Im am planning to fit an H165 diff (ute rear axel assembly) to my 1200. I read somewhere here that these diffs have a different tail shaft flange. If this is the case, do ute tailshafts use the same size universal cross as the cars? As in, can I fit the diff yolk off the ute tailshaft onto the car one? Or does the ute use a bigger universal? Would the tailshaft be the same length from a GB120 (long wheelbase) ute to a car?

Well, in the Aussie market. . .

The Utes had larger replaceable Uni joints. The Flange is bigger. Gearbox splines are the same so the best option is to retube a ute tailshaft so it can be rebuilt if needed. Well that was my logic.

Yep I'll second that - Cable_Tie is spot onn.
I have been through all this in the last 6 months and I can tell you that the quickest and chaepest option in the long run is to use a ute tailshaft with the bigger replaceable uni's and either cut the tube to suit or make a spacer if it's too short. From memory I think the ute tailshaft that has the double tube with the rubber insert will fit straight in once you make a 20mm spacer and fit it at the diff end of the tailshaft.
If you use a standard coupe tailshaft you will have to shorten it approx 65mm to suit the ute H165 then make an adaptor to suit the different hole centres between the H165 ute diff nose and the standard coupe tailshaft uni flange.

Does anyone know what the wheelbase of the longwheelbase utes is?