Originally Posted by
stronglight
Check near the bottom of the post for any imprints. They often stamped both a date code and the diameter size of the post just below any limit line markings.
According to Trek's online catalog, they used a SR (Sakae Ringyo) "SR-P5" Laprade style alloy seatpost. From my own experience with similar posts they indeed had quite short shafts.
Here is a photo of one similar slightly fancier model from SR.
This one is a few years older (1980).
This particular model has a shaft only 170 mm long
... only 190 mm from the bottom to the saddle rail.
diameter should be 27.2 mm. The length should be around 250 mm or so.
I can see not liking the aesthetics of a Thomson, but it you need setback, your knees pretty much require it, but it doesn't have to be a Thomson of course!