I sent the following message to GM Heritage
Hello,
Some of the vintage Chevy truck owners have noticed that there is a MBC stamped on the bumpers. Is there a record of who manufactured the bumpers for the Advanced Design trucks? I did find that there was a company called Michigan Bumper Co that was bought by Gulf Western in 1958. Any chance that the MBC means Michigan Bumper Company?
Sincerely,
Paul Stanley
Maple Ridge, BC

Their reply was. We don't know the answer, sorry.

A day without laughter is a day wasted- Charlie Chaplin
When wrestling a grizzly bear, you have to keep at it until the bear gets tired, not when you get tired.
1948 Chevy 2-Ton