have specifically said their gear sets can't go in a case that had already had a Harley six speed gear set installed.
was it specific? or a like the trans engine side cover will not fit with hydraulic clutch covers and the quick disconnect fuel line will not work on touring bikes answer?
Vague and generic.
Like I said, have not done any work on our transmissions, but I have worked on a manual trans or two.
And I have seen many manual grenade themselves internally with little or no case damage.
Of course I have seen the opposite on some apps. Wasn't uncommon in the late 70's to see gear boxes blown apart, especially with 440 6 paks or hemis.
You might get lucky here and just have a gear that decided to self destruct, doesn't take much to lock of the gear set, just put a chunk of metal between two gears.
Try contacting Jim's yet?