I think the smooth idler was introduced later. Some early images of AMX-13’s (development, trials in Sweden in the 50’s, other variants) show other types of idlers. Most images of IDF AMX-13s have the smooth idler and Singapore got theirs when IDF replaced theirs with heavier tanks (late 60’s)
The AMX which raised the question:
An IDF AMX on display at “Yad La-Shiryon” armor museum:
Looks like an official portrait photo taken during evaluations or something:
Photo from trials in Sweden when we were loking for something modern. Sweden ended up reworking older tanks to make the Strv 74 which wasn’t totally successful, ahem … say no more … :
French AMX-13 DCA:
and another one with smooth idler
AMX-13 with SS-11 missiles (looks like some trade exhibition … ) :
Singaporean bridge carrier.
French Poseur de Pont:
(looks severely top heavy …)
Another one from Singapore:
(looks like a different riser plate or am I just imagining things ??)
Edit: see Oliviers post about idler history below