I'll support your initial assumption for Century - due to some little details on serifs...
More specifically it looks to me like Century731 BT (Roman) from Bitstream.
The numerals ("1950") is also an accurate match for Century while they are totally different in Excelsior.

Presumably the image is from a Mechanix Illustrated from the 1950s?
Numbers are wrong for Excelsior but are closer to Century 731 BT , available since 1929 as Textype, http://www.myfonts.com/fonts/bitstream/century-731/ Also Egizio, but 2 is off, http://www.identifont.com/show?618 available since the mid 1950s.
Still checking.
Don

Thank you! I've compared it to Century 731, and it does look very close. There were different versions of Excelsior to which I compared it originally, and some had numerals that did seem to me to match, which is a reason I chose Excelsior over other members of the Legibility series.

But Century 731 is wider than Century Expanded, so my next question was, what is Century 731 really? So I did some Googling.

ParaType told me the face was part of the Legibility series, and originally designed by Chauncey Griffith.

And then Identifont yielded the secret: Century 731 is Bitstream's version of Textype. (Chauncey H. Griffith, 1929.) So I'm going to check out the original, since Mechanix Illustrated was done on Linotype hot metal equipment, after all, which would account for small discrepancies from Bitstream's digitization.

Well, I managed to hunt down at least one image that included a specimen of the original Textype; here's a piece taken from that image:

And here's some more Textype, with a lot of digits:

The second sample, though, seems to have a smaller x-height than the first, as well as being a better match. However, I did come across a source that mentioned that there was a "book" version of Textype as well as the "newspaper" version of it, so I could well have encountered both in that case.

I was amazed to learn of a Legibility series typeface which, despite having often seen, I had never heard of (by name).

I saw it turn up, after this thread, in a Google search on an unrelated topic:

The instructions World War II pilots had with them on how to use the Norden bombsight!