Oh dear... this can't be good... I find myself in a strange place right now... I am in agreement with a Trident rider!
Seriously, I do agree with you, the bike as it is, really is a well balanced package and, as you say, too much enhancement in any direction would open up that same can of worms that the Trident Hunter came from!
And I ain't going that route!
Possible deviations from stock that I had toyed with are:
1. A belt drive. Nothing wrong with primary chains, I just like belts better. And ditching rotating mass in the primary would complement the lightweight crank I think. So this is a possibility for winter.
2. A 5 speed gearbox. The stock triumph 5 speed box is lovely, and a peppy 650 would benefit from it better than a 750. Trouble is, the current 4 speed job in this bike is really so sweet, so I can't see me changing it.
3. A Routes style 750 (ie stock looking barrel) I think that so long as the Pistons were lightened, a 750 block should enhance low to mid range grunt without any significance down side. But this is only something I'd do if / when there's no re-bore options left for the stock barrel.
So unless a failure of some kind necessitates replacement, I think the only nicety on the shopping list is the belt drive.
Some general comments on the bike now I've put a few miles on it:
Firstly, no wonder they were so popular in the day! Compared to a Commando, even my Trident Hunter which has shed a lot of weight, the T120 just feels SO light and nimble. Around town (in Oxford) it's a real blast! And out of town, it blasts up to a ton so easily.
Alan said that when he rebuilt it he didn't have the crank balanced as it was already so smooth. And he's right, it really is surprisingly smooth, so much so that I'd guess someone has dynamically balanced it in the past, but who knows, maybe it was just one of the 'good uns' that the law of averages produced on occasions!
Anyway, enough waffle now, I only popped in for a quick cuppa, the sun is out and I'm off for a blast through the Oxfordshire countryside. Life is good. Catchya later...