Hi Nexxussian . . .
I don't believe that babbit rods went away until full pressure oil made the scene. But rods could be converted by a machine shop so inserts could be fitted. But it implied specific machining on the crank throws because shims should not be used with inserts.
D Winn . . .
I did a little more leg work. It appears that Chevy continued to ship the 216 on trucks through '53:
Old Car Manual Project .
So based on a little reverse engineering from my Master Parts catalog ('49) and my Hollander Interchange ('52) I am surmising the following 'rough' progression on 216 castings:
'49 3835253 (in my '49)
'50 3835497 (in a '50 I almost bought)
'51 3835527
'52 3835794
'53 3835849 (trucks only? which is what you've apparently got)
So perhaps your original hunch is correct. Not sure if the factory fitted those insert rods - but they would have certainly been available.
regards,
stock49