Verne, the quote from above is from the link provided above as well, they also state that the one piece bumpers went through 1964 ...
"This'll give you something else to look for: I've seen one-piece bumpers on California cars from 55 to 64 (the full-size cars). They're nicer looking than the two or three piece bumpers, because they have no visible seams. "
I am not an expert on early 60's Chevies, so I couldn't tell you if 64 is fact or fiction ...
Here is some info on the 57 one piece bumper from a Hemmings article:
"Most front bumpers were three-piece units, but even in 1957, California law prohibited this, and all new 1957 Chevys delivered there had a one-piece bumper."
linkie:
http://webcache.googleusercontent.com/se...p;client=safari