Having been made aware of the HAER and HABS resources (thanks to Chris), I found a whole bunch of drawings of plans, elevations and cross-sections of various Alpine Tunnel buildings:
http://www.loc.gov/pictures/related/?q=Colorado--Gunnison%20County--Pitkin&fi=places&co=hhAnyway, thought it might be of use to someone....
Cheers,
Jeff.