I'd like to see some documentation of GMCs delivered with Buick engines. Some heavy duty (2 ton and up)'55-59 Chevies came with Buick engines and some heavy duty '55-59 GMCs came with Olds engines.

I'm assuming the OP has a pick up and not a big truck. It would have come with either a 270 6 or 347 8 of Pontiac lineage.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.