Fitting R31 rear discs

You use the standard r31 caliper mounting bracket
One bolt hole lines up with the h165 or h190 disc/drum/axle flange bolt holes. so 3 new holes need to be drilled to suit.
Then you need to weld some plates to the inside of the caliper bracket centre hole so that it can retain the wheel bearing in the h165/h190 as the centre bore is only just smaller than the OD of the datsun wheel bearing.
Therefore it will technially retain the bearing but there isnt a whole heap of meat in the bracket doing this job so its best to ad some more.

Caliper offset is spot on by some fluke, and depending on whether your axles have a centre locator for the disc of not the disc or axle might need to be modified, either hole enlarger or axle locator made smaller

The handbrake cables are a little more tricky and i havent got around to doing that, just a matter of figureing out how to best adapt and modify the r31 cables and splitter to the 1200, or you just swap the r31 calipers out for vn-vs/vt or whenever they decided to go to a different rear caliper and run a hydro handbrake setup

Have done this setup for my car once upon a time and for adrians car