The semi-fluid grease is good for older gearboxes which were specified to be grease-lubricated or which had no effective seals. On the Douglas I just filled it right up using a 50ml syringe and the surplus worked its way out past the mainshaft and lubricated the primary chain most effectively (and the silencer and the new drive after a run...).
Newer bikes like my 50's BSAs and Norton 99 used SAE 50 in the gearbox, though that is pretty much the same viscosity as EP 90 gear oil. I either use SAE 50 or classic EP90 depending which tin has most in at oil change time. Not very scientific, I know. The Norton gearbox has covered 220,000 miles on this regime, the only failure being a layshaft bearing which is a common problem on Norton gearboxes.
Best of luck with the Douglas - ours is great fun to ride - the other bikes are tending to gather dust!