My understanding is that 1-1/8 (going by memory, pretty sure 1-1/8, not 1-1/4) front and 7/8 rear is indeed stock on our 71s. In addition, CCOT has told me that they sell the 1-1/8s as an upgrade over the 7/8 for the rear. I have used them (indeed they are installed right now) and can say they have worked just fine for several years now. I will also say that when I ordered in replacements from NAPA (after dealer informed me that they are officially unobtanium), they DID NOT FIT. I had to take them back, which is when I got the CCOT units. NAPA's parts book said they would fit, but when I tried to install them I found the hydraulic fittings all wrong. 1971 is a funky year for Land Cruiser drum bakes, things became much more standardized on later 1970s wheel cylinders. As I wrote before, I would trust Mark for the exact right parts for exact stock for your month/year build. But, as I wrote above, the CCOT parts are working for me right now.
The primary downside to the CCOT parts is that you can not put a flare wrench on the bleeder fitting because of it's recess, although a regular open end wrench works fine. I have not had an issue with the larger bore causing excessive rear braking, although there is slightly more pedal movement required due to having to move more fluid; it is not a major issue and is easy to get used to.
For everyone snickering and about to make the "switch to disks" comments, once you have your Land Cruiser drum brakes properly maintained, they work just fine and will put your nose on the windshield. As for wet braking, I have been pleasantly surprised by how well the brakes worked right after fording the South Platte on Hackett Gulch. And shoes last at LEAST twice as long as pads in my experience. I have to adjust my cylinders on my drum brake Land Cruisers less often than I have had to replace pads on my disk brake ones. In my experience, the main advantage that disks have is not having to adjust them. One of these days I might try the later model runner calipers with the dual pistons and see if they are that much of an improvement over the single piston units.