A full-flow oil filter was supposedly standard equipment on 1962 261 engines.
Check out the following section/pages in the Specifications Manual:Scroll way down to:
Engine and clutch: pages 11 and 12.
There might have been a bypass oil filter RPO. RPOs are not shown in that Specifications Manual.
Or (clutching at straws with this statement): you might have a replacement engine that came setup fo bypass filter, but was able to go either way..
