Well I figure the most important thing is the fit, which is excellent for both my stoker and I, and second would be quality of construction which is, again, excellent. I have several bikes from the 80's which I enjoy riding immensely even though they would no longer be considered cutting edge, so the age of the bike does not put me off.
Not that it would have any impact on my buying decision, but supposedly the bike was ridden to a gold at one of the National Masters time trials. If that is so, then it would seem to be a fairly good performing bike as well. I wonder how a person would go about verifying something like that? Doesn't matter, I'd buy it even if that weren't true, but it's amusing if it is.
Oh yes, and I realize that the performance of the engine is more important than the performance of the bike, but I would imagine in an event as competitive as a TT the bike still something of a factor.