Hey There Left from Salt!
I see that You are a NEW MEMBER
I am also a proud owner of a '56
Your '56 uses a pretty common oil filter for the Era. Like most GM's it uses an A/C P 122. It is a perferated metal canister with a gasket. Not much variation or diversification in size. It is the one size fits all.
Most parts houses can get their hands on one but you will probably have to order one in advance and have it in a day or two.
Personnally I do not use Fram Filters. They have a high failure rate.
An improper sized filter will cause the problems you are experiencing.
Hope this HELPS! You out.