Serial numbers are a very easy way to tell.
If the number is three or four letters and then some numbers, then it's babbited.
If the number starts like this: GAA, ADCA, et cetera, then it's a 216 from one of the various different applications. the second to last letter will be "A", "B", or "C"
IIRC, if the second to last letter is a "D" or an "E", then chances are, you've got a 235.
There will be date code behind the starter.
Later Chevy 235 (full-pressure oiling) engines will have some numbers, then an "F" or a "T" two more numbers (the year code), and then an engine use code (usually a Z or a ZC or something like that). In 1958, they changed things up a little bit, and there isn't really a "serial number" on the engines, but there is a date code.
There is a tech tip on this website you can have a peek at that will give you some more information on the Chevy engines.
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GMC engines will have the displacement (e.g. 228, 248, 302) first, which will tell you what the thing is. IIRC, all of the GMC engines from that era had insert bearings and were full pressure oilers.
