While the RB-2 is not as highly coveted as the RB-1, I think it's similar enough to make it a much better bargain than the RB-1. Looking at the catalog for that year, it looks like the tubing may have been identical to the RB-1. They are both Ishiwata triple butted tubes, which is very good stuff. I guess their tubing was 'proprietary' to Bridgestone, which may mean it was high end but offered on a bike that was at a lower pricepoint, hence an agreement not to use Ishiwata tubing decals? I don't know. But it's likely as good as most of Ishiwata's high end tubing, which would have been 019, 021, or 022 most commonly. You can search those tube names to find more info.

At any rate, the RB-2 I had was a nice ride, even on the cheap wheels it came equipped with. Stiff enough, but not harsh, good acceleration and a good climber.