TTI five speed box question...

A close ratio gear cluster for a 4 speed Commando box costs about $700 and any AMC first gear will fit. A 5 or 6 speed TTI box costs about $5000. If I had a road bike, I would go fort the first option and live with the gap between 1st and 2nd. You probably would not even notice it.

Yes but I already have the TTI box! The only time I use first besides starting off is in traffic or on old green lanes. The engine has plenty of torque to
pull a big gap between first and second.
Im leaning toward a new low speed set which would leave everything else as it is.

As a confirmation of the actual first gear ratio fitted, which seems to be around 2.4, you could try this I got from TTi, regarding what they tell me is a 2.44 ratio in my box:

'To determine your ratios accurately put the gearbox in first gear, turn the output sprocket 10 times and count how many times the input shaft turns. It should be 24.4 which gives the ratio of 2.44.'

Bruce seems to usually supply 3 countershaft sprockets with each TTI box. You could try the biggest and work downwards. That way you would only be shortening the rear chain. Most of what i do when changing gearing is 'suck it and see'. Once you have a starting point, you will know what you are doing. Fiddling around with the numbers does not really tell you what will happen in practice. One ride on the bike will tell you a lot. But when you do it, you need to find a stretch of road where you can repeat the exercise several times, preferably with a variety of circumstances.

With a road race motorcycle, the gearing is usually different for each circuit.