That's my recollection too, Paul. With both Mick and Birks developing these bikes over such a long period and with such a large team, as the Hamilton Team was, I guess that 99% of the development that was to be done, particularly with the engine, was achieved back then. OK, Trials and riding styles have moved on in 20 years, but to such such a degree that would make that development obsolete? I doubt it.
One bike I do remember which was right at the VERY end of the Hamilton line of TYR's was one that "Wee Pagey" rode which Mick was developing. I don't know if any of the rest of your team tried that or similar configurations, but I recall is was a short stroke version - around 230CC? I remember this being a "stop gap" before the TYZ came out to try and give the TYR a snappier more "modern" response. Not sure if David ever rode that version in anger but I certainly remember him riding around on it at his home. If someone is wanting to make their TYR's engine behave in a "more modern way" then I guess this might be something to look into.
If I were ever to get another TYR, then I would want it to the spec of Mick's bikes. The 270 I had with shortened inlet was just so soft and just kept pulling liked a tractor (in a nice way). Nothing compared to today's machine and still outdated at the time, but for a TYR - LOVELY - and great for belting along the roads at the Scottish!