The difference between those two part numbers is just the revision #. From what I can find on Twin motorcycles and St. Paul lookup, you do have the correct part #.
https://st-paul-harley-davidson-buel...ing-models-u6a
https://www.twinmotorcycles.nl/websh...sp?mc=1&aid=59
It looks like you found the correct size/pitch for the threaded portion... I still recommend getting a bolt that size and threading it into the hole. It may just have the first thread or two buggered up from removal. Or Cooter worked on your bike. If you can thread the bolt in easily, the threaded portion should thread in easily as well.
Lastly, download a free manual from Buellmods.com. You did remove the 3 bolt inspection cover and clutch ramp assembly beforehand, right?