Hi Nick,
I’m not sure if/when AC switched to the end caps shown in your pics (during or after production). Here’s a pic of my front bumper showing the original style end caps on top and the replacement end caps on the bottom (that came with replacement bumpers, which I believe were ordered from the Works in the late 80’s). Btw my new bumpers are stainless steel along with the end caps. My original bumpers were chrome plated. My car is a 55 Aceca. A local friend with a 59 Aceca has a similar mismatch of bumper end caps. Perhaps someone else on this forum knows about when the switch was made?
Let me know if you’d like some more detailed pictures and measurements of the early type end caps. I’d be interested in getting some of the early style end caps if you decide to have some made.
I hope this helps.
John