depending on which gear ratio set your 6 speed has,,, determines the differences..
an O.D. 6 speed,, will have a .86 or .80 6th gear,,, 1st gear can be 3:24 or 2:94,, the other 4 gears are the same ratio as the harley gearset.
a plain 6 speed,, depending on the manufacturer,, can have any combination of gear rztioz,,, many having 6th as a 1-1,,, these gearsets,, just add another short, to arrive at the same point in 6th as you had in 5th before..
ultima transmissions are hit or miss as rare as quality is concerned.. as mentioned already clearancing my be necessary,, as the shift forks are thick on the shaft end,,, due to them being cast... on mny ultima trans Baker shift forks and drum may be exchanged for the ultima set,, as well as the shift shaft with stops built in... this fight and up the very long throws of the ultima shift mechanism. some have shifts so long it feels like you went back to a pancake top 4 speed...
I dont use ultima transmissions... they may be ok on a stock engine,, but add some power,, and problems may arise,,,
I've worked on enough ultima transmissions to have formed this opinion,,, I see what looks like casting flash on the flat edges of some if not all of the gears,,, I wondered how they could be made of 8620,, and my conclusion was,, that scrap and machining droppings were re-melted then cast,, to decrease materials costs,,, this would be considerably less expensive than buying bar stock 8620,,,, can't prove it,, but???
Baker gears and shafts are cut from 8620,,(by andrews), and look perfect,,
it would seem ignorant to me to spend more on the shift mechanism than the transmission cost.. I would save up for a Baker kit, and be done with trans issues forever..
i