Internal gears - Alternatives for 92 610TE

I have a Supermono road race bike powered by a 610TE engine. It was supplied with a 6 speed gearbox (reportedly sourced from an early model Husky 125) as a race ready package. We developed the engine with a dry clutch, downdraft head and big bore 630 cc. It was very fast and won many races.

I plan to bring the bike back as a historic racer but want to undertake some preventative development first. The gearbox is the weak link, particularly 2nd gear, and would be helped by: (1) installing a later/stronger husky 6 speed gearbox (maybe from the WR 260 2 stroke if it fits), (2) installing a primary gear set that would speed up the gearbox and take some of the stress of it, or (3) both the above .

Are there any suggestions out there as to what parts could be used.

2 stroke gear boxes won't fit properly in a 4 stroke motor.
When you pull it down sent me pics so I can see what you have.
Later George

George is correct, we need to see more pics at least of the other side at this point. Maybe some close ups as well.

Racing the superkart this weekend and preparing the H2R and the KGM for the Barry Sheene so I will be a few weeks before I get down to taking some close up images with measurements. Thanks. This is a picture of the other side - but probably won't help. Back in a few weeks.