It could have a left or right hand thread.... It should be stamped on the part that engages with the speedo dogs. I know mine was opposite to what everyone expected. Underneath it there could be one or two steel washers and a felt seal. Mine had two but when assembled it would lock up the speedo drive. I removed the outer and reassembled and it was fine. The extra washer made the spacer in behind loose axially so that the speedo drive outer couldn't clamp up against it. I have a 1966 & 67 parts book, the 66 has one spacer, the 67 shows two.
Anyone want an old Clymer manual before I use it for toilet paper? LOL
Keep it! You'll probably need it. Each publisher sees things differently, and having all versions of "home service manuals" is the only way I've found to cover it all.
For example, I remember in BMW world, the Clymer walks you through the rear end rebuild, while Haynes blithely tells you it can only be done by a shop. Or maybe it's the other way around, but on other issues it's the reverse. Never found one that covers everything.