I dont know if an actual retrofit kit is available but what I have done(from feeble memory , FWIW) is simply buy the tapered bearings from an industrial bearing supplier to fit the top and botto of the stem, as I recall they are different diameter , and turn some cups to mate the ID of the frame to the OD of the new bearing . Preetty simple , but you will end up with a gap that might make the stock headlamp mounting ears look awkward . I have found that the Triumph covers seem to fit well .
Again from a feeble ,memory, you can get some Timkin bearings with the correct ID but the OD is 2.25" instead of the 2.125" needed, I got the OD ground down. The length of the bearing is also greater leaving toofew threads engaged at the top, so I got the inners shortened by EDM machine.
If its of any help SRM in Aberystwyth,Wales do a direct replacement headstock taper bearings for the pre-oil in frame A65. As I remember they cost about £65 for the set,apparently they manufacture the bearings themselves.Their email address is www.srm-engineering.com.Cheers,Paul.
I've done this mod on Triumphs and there is a noticeable gap between the top of the headllight ear and the top tripple clamp. Frank said that it's the same thing with BSA. He suggested installing an Oring there to take up the slack and prevent water from getting in. The bearings should be arriving this week and I will post what my final cost was.
still not a ridiculous price if they are a good fit. I used the stock ball bearings, tightened them just enough to stop the fall-away of the frontend, and now they have some bad flat spots(ratcheting). I dont want to buy another set of races, so this deal is the way to go, especially to prevent problems down the road...
If you remember, throw up a quick post once you get them installed, and let me/us know how they fit and work.