I lean toward a vacuum operated brake boost picture 2 above. Attached is a photo of a PCV set up for a 261 I found and cleaned up (for the curious).

First pic: end would attach to manifold.
Attachments
5147A56D-C3F4-4814-9A39-7CFAFDDC407A.jpeg (224.46 KB, 238 downloads)
10CE219D-EEE4-4A19-A429-033882F4E81B.jpeg (245.13 KB, 238 downloads)

Last edited by tom moore; 03/16/2022 10:08 AM.

1946 GMC Project
"Back-in-the-day Restore"
Read the story in the DITY Gallery