a 27.0 seatpost is not a surprise if that's the correct fit: this is a 60cm frame and with that size it's common to use the heavier-wall SP tube for seat tube, maybe other tubes as well but probably the remainder is SL tubing.
Same decal was used with either all SL, all SP or a "mix".
the story long recounted as to what was actually used in that World Record run is that despite what the frame said he rode the bike he wanted to use, and it was not a Mexican-made Windsor!
But Acer-Mex paid for the event so got to use those World Champion Stripes!