Interesting - have lots of books but not that one and I don't try to be an expert. Also have/have had T120C, T120R, TR6C, TR6R, T100, T100C, T100R, all unit construction, but none unmolested so it's hard to say how they left the factory.
Several sources say the T120R was the US T120 and T120C was the high-pipe competition (off-road). It all gets confusing when you add TR6C (road completion?) and TR6R (road). My TR6C definitely came with E.T. Ignition and high pipes as did my 66 500 (bike stolen in 1970, don't remember the model identifier)
The first parts manual I have that lists the T120R was published in 9/68 and is part SPC.7 which is the US version of SPC.9 which is the UK and General Export. As far as I can tell, there was none just called Catalog 7. Catalog 6 does not differentiate in intended destination, and Catalog 8 is like Catalog 6 in that they only list TR6 and T120.
Also, they were inconsistent between the 500s a 650s. T100C (US low pipes, 67 on, I think)/T100R (US Low pipes 67 on, I think), and several other suffixes earlier on.
