So GM did not have enough smog ready engines in the late 1970's. The small block 350 Chevy engine found it's way into other GM car lines. Customers complained, "I got this expensive Buick with a Chevy engine" So GM painted all the engines black. Most customers didn't know one engine from another, except the color.
Yes I remember when the "corporate engine" shenanigans started about 77-78.... We used to have a favorite restaurant in SW Houston that was next door to Frank Gillman Pontiac/GMC, and every year when the new models were dropping, we'd go check em out after supper. This may have been around the time we bought the parts store and were looking for a new shop truck, which would be May/June '78....
Anyway, Dad was looking at several of the Pontiacs on display, and knowing the differences between the various GM engines, he starts asking the heretofore very helpful salesman questions like "I see this new Bonneville has a Buick engine in it, could you give me a little information on that?" That salesman about turned green and purple, he had strange looks on his face, and he went to the office and we never saw him again that evening. None of his coworkers would talk to us either....
But then this is the same dealership that couldn't figure out what color of metallic brown to paint the eight foot long rear fender on the '81 Sierra that we bought, that allegedly "got scratched being unloaded from the transporter" and didn't know that the front fender/wheel well trim on an '81 were different than the '80s.... several months into the model year. And remember GM was really pushing that new front clip, aerodynamic to compete with the Phords.....
Anybody in the greater Houston area that bought a vehicle from them, or knew someone who did, has a Frank Gillman story or two....
They were legendary here, and mostly not for good reasons.