The tee at the top is the early one, with the casting number 51910-52 on the other side. The tee at the bottom (casting 51910-52A visible) is the later one.
The rear halves appear identical. But you can see that the front halves are different in almost every respect.
It looks like the early version of the front section of the Tee was used on both the 51902-52 (1952-1953) tee, and the early version of the 51902-54 (1954-1970) tee. Then the later front section was used from about 1959 or 1960 until 1970, when this kind of seat/tee were retired. The casting marks (other than the numbers) are very different between the two versions, possibly indicating different foundries. The later ones appear much stronger, although one wouldn't expect that to be an issue. Perhaps they were just less expensive to manufacture that way.
sportsterpaul wrote:I just got the new Captcha question "Magneto Sportsters ALWAYS start on the _____ kick:" and it does not seem to work even though I typed in the correct answer: Thirtieth.
Paul - yeah, and I was stunned when Alex Trebek allowed "Alice In Wonderland" as the correct answer to "What is Lewis Carroll's most famous book?"
The big goofy spacer? The 52105-52 is .875 diameter and .550 tall
Oh, you can see in the photo that the seat/tee I just bought has a CP 1038 front bolt, but the two rears are Circle-Fs. My XLCH has CP 1038 front bolt and hardware store rear bolts. Can't really vouch for the rear bolts.