Wrenchman, Below is screenshot from an out of stock 1927 GMC T40-T50 advertisement that has a very detailed illustration of the Buick I6. From what I've read, that engine for the larger trucks was the 274ci model, while the engine used in the T20 1 Ton is noted to have the 207ci Buick I6 (from Gary's 1927 Fire Truck article in my reply above).

There are some 1927 Buick engine pictures in this AACA thread that may be helpful in the future.

Also came across this original 1927 Buick manual that may be of interest and could provide some additional info on your engine too. Best of luck on locating all the parts and pieces of the truck! thumbs_up
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~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)