I would still be careful with the shifts, particularly the downshifts and treat the gearbox w/ respect.
Its still possible to damage a GB with a cushdrive, as I found out buying an old bike.
I found chipped/worn gear dogs and bent shift forks, had to make one out of two. Should be testing it very soon.
This was a 2 stroke street bike box fitted with cush drive. There is a known second gear problem, but its caused by abuse.
Edit: better pic