bamboobike4

Good point.
I'm figuring weight-wise, closer to the Ironman (only 2.2 oz diff between Ironman Tange 1 frame and Lemans RS Tange 2 frame in 58cm).

Geometry, looks a little closer to the Lemans RS and Elite RS, both of which were raced as much as the Ironman in the mid-late 80's.
The Ironman looks like it tucked that back wheel in a little closer, but the more I look at your pics, it may be a twin in most ways.

At least half of my "racing friends" chose the Lemans RS and Elite RS, mainly due to cost and the ability to use the $250 savings on components.
With the Elite RS using the same 600EX as the Ironman, it was kind of a no-brainer at the time to save the money, get an Elite RS, and upgrade.
You could get an Elite RS, those new-fangled Look pedals, and a set of aero bars and still be cheaper than an Ironman, just not an icon.

In any case, could be the best of both worlds. A Tange 2 Comp T/A, in my experience, was a more suitable frame if you decided to ride all day.
Doesn't mean I've not ridden an Ironman on at least a dozen centuries, but I relaxed a bit more on the Comp T/A, and a 7700-equipped Comp TA is a smoothie.

I've seen few Nishikis, but those I've seen had excellent durable paint and the same quality as the Centurions and Japanese lugged Schwinns of the era.

54cm TT and I'd be interested. Those are interesting colors to work with. Would be a great bike to "see what it's got" with modern components. My thing.