Bumper identification - smooth/no groove 33-36?

[rockfla]

As they say, curiosity killed the cat, what about the "large" trucks, IE Model 51's, I would assume either the knowledge that has already posted here and or Dave (Model51), Newc or GBSisson would have chimed in here to let Us know IF they were for the BIG trucks, panels, firetruck, etc etc???