The previous owners of both my 54 KH and 62 XLCH are tall - 6+ feet. The 54 had the original horse-hide buddy seat on it. The 62 had the original Dual Seat. Both said they were uncomfortable with the solo saddle. I replaced them both with solo saddles.
Check out this page:
https://www.harleykmodel.com/technical/seats-buddy/index.html It was supposed to replace the current Technical:Seats article, but it failed to make it to the index. I don't know why. Click on the illustrations on that page.
If you need more room, your 1955 could have the version 2 buddy seat shown. These are a little hard to find, but they are out there. There's a repro (V-twin?) solo saddle being sold that appears longer than the stock saddle, possibly more like the 52000-40 saddle used on 1965-1969 XLCH. I've never investigated that one.
All the seat tees will fit on all the 1952-1969 bikes. BUT, the 52-53 seat only fits on the 1952-1953 tee. The 1954-1964 seat only fits on the 1954-1964 tee. And I think the 1965-1969 seat only fits on the oddball tee (51901-52R ?) tee.
Mr. Iron(II) - isn't the 1952-1953 seat a little shorter than the 1954-1964, and it has a "cupped" shape that gives the back of your butt a little extra support? You know, the awesome power of the 750 cc Ks would blast you right off the seat!
TMcC - 1955 KH, NZ, did you ever meet
Michael Broad?