Here's a couple more I found of my 65 when I was restoring it. The engine was clean and had over 100,000 miles on it and you can see the separator. Cleaned right up and reused it on new build. The other picture location of the vent tube installed.

Also all 265-283-327 blocks had these. Some years and model Chevy's used a pvc valve that screwed int he back of the carb along with the tube. It wasn't until 69 when the 350 block come out that these disappeared.