HO drawings of FA-1 are in Model Railroader for February 1969. Railroad Model Craftsman for August 1973 has an article about the detail differences in the first FA-1, built for the GM&O: the article is about modifying a commercially available model of a standard FA-1 to represent this variant, with an undimensioned drawing. (One useful thing here: some of the carboy trusses are visible through the screening at the top of the sides, and the drawing marks their location.)
The two-part Trains article on the FA (both FA-1 and FA-2) mentionedby S1f3432 is in the June and July 1975 issues: lots of photos and some data, but no drawings.
Alas, I fear that none of these are good enough for the purpose of large-scale modelling. Ideally, of course, you would want photocopies of the original Also-GE plans! I think it likely that these have survived, but I'm not sure where you'd go to look for them. I believe that when Alco left the locomotive business, a lot of papers were donated to the library of Union College in Schenectady: a reference librarian there might be able to tell you whether they COULD help you. Another possibility is to find a preserved FA-1 (I think the Railroad Museum of New England, in western Connecticut, and the national Canadian Railway Museum in Delson Quebec (outside Montreal) have FA-1 units) and visit it with cameras and tape measure!
My guess is that the dynamic brake hatch and the circular radiator fan housing -- two of the most prominent roof features -- would be the same on the FA-2 if you can't get detailed images specifically of FA-1.
Sorry I can't be more helpful. Your project of a 1/8 scale FA-1 is marvellous; thanks for posting the under-construction photo in your first post!