I have a 1955.2 Series GMC Shop Manual (X-5503) dated October 1955 that lists the driveline options for all models 100-500. According to the listings, Models 100 thru 350 list the 248's as what looks to be the standard engine with a 288 V-8 option. Various model Hydra-Matic transmissions (models H-M177C, H-M210U and H-M220Y) where offered in this model range.
The 270 6 cylinder and 288 V-8 are listed for the Model range 370 thru 410, all with either Hydra-Matic Model H-M220Y or standard 4 speeds for transmissions, with an optional 5 speed manual (Model 205V).
Just a guess on my part, but I think the 270 in his truck is likely a transplant from a bigger truck, but still maybe a 1955 original model year.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "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)
