is a sedan diff H145 suitable for a 1200 ute??

Should be ok but not as strong. Best stick with the ute diff.

it seems to be smaller too, the diff in the ute is f*****, so much backlash, i doubt its fixable but not sure?

The 1200 sedans and coupe use H145 diffs. The ute's use H165 diffs. The inside diameter of the ute diff. is 20 mm larger, and uses a different housing. So NO you can not use a sedan diff in a ute without changing the whole assembly. Not a smart idea as the ute diff. is also stronger.

Is it possible to recondition the h165 diff then???

Yes, it is possible. But more reliable and less expensive to swap in a good used H165 center unit. They were used by many Datsuns.

Where can I get a diff centre from? Or do I have to hit up a wrecking yard?

Yes, the usual source of used parts is the wrecking yard. But you can also buy them from club members, gumtree, etc. Best to buy one straight out of the car, not one that's been out and sitting in the yard for years.

Ok thanks, will I need to changes the axles aswell??

Hey maddatter no your wont need to change the axles only the centre.spewing the sedan diff won't work