I've heard they were found with a 27.2 or (early versions) with a 26.8 seat post but possibly even a 27.0 in 1970's era Acer-Mex "Pro" if something like an SP seat tube was used.
Also typical for that era would be a semi-sloping external-socketed fork crown (sort of like the Cinelli Model B but not exactly) but I've seen a few with a "Cinelli SC-like" full-sloping internal socket forkcrown (not sure if those examples were something after-market like a Tange replacement or made by Acer-Mex)
Plus the serial number on Windsor/Carabela Pros would typically be stamped on the side of the seat lug, usually the LH side, not on the BB shell.

All details subject to change and "exceptions prove the rules"