1200RC
God i love this forum as it is a constant learning curve for me too.
I didn't know that the disc brakes fitted the ute rear axle.

The next trick is to try to match up the front discs, & late 200B used the same spec caliper as the Bluebird [same pad too] so 200B struts should fix that one.
I dont know what master cylinder works best, but series 1 Bluebird & late 200B used the same bore size, & had the same brake bias pressure of 450lb's The series 2 bluebird used a 550lb bias pressure & need the correct series 2 metalic pads to work as per factory specs.
The 200B Vac chamber is the smaller of the two & may prove to be a good choice along with it's attached master cylinder.

This setup should prove to be a serious brake system for a road going "improved performance" 1200 & it's ALL made from standard Datsun parts. WOOHOO

What i want to know is whether the brake mounting flange is the same for the smaller 1200 rear ends. That is to say, will the disc brake mounting plate fit the smaller Datsun 1200 & 1000 housings.
I suspect not, but one never knows unless one asks.