There is a bushing at the end with the bellcrank. Parts book shows a 'clutch release shaft bushing' in Group 0.795, pn 1356209. A quick search on Google, Buick Farm, and e-Bay didn't show any hits.
Fairly sure the other end is metal-on-metal. Buick did add a grease fitting in the cap plug to lube it, but early cars didn't have the fitting.
Here's a pic I have on file of the shaft bushing: