Take a look at this thread:
https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=95774#forumpost95774 Jim (39Super8), did a bunch of research on the 356 oiling filter/pump and the running changes that were in place between the first 356s and the last ones. (jiggle pins, pumps, different filter plumbing, etc)
The early 1940s filter were plumbed with the inlet on the bottom of the filter and the oil filtered from the inside of the filter out, and the canister had an internal check value that would pop open to bypass the element if it got clogged.
That changed that later and went to a bypass filter arrangement with the inlet on the side of the canister. Also, if you look at the later oil pumps, the move a lot more volume than the earlier pumps. That was the final "oiling" fix for these motors....more oil volume being pumped.
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