The oil canister and filter cartridge was an option in 1956. It's not uncommon to find an engine without a filter.
The bolt in the cover is captive. It's designed to stay with the cover. If the cover does not want to come off, then rust, sticking gasket or sludge is holding it down. When you get it apart, make sure the parts inside are in the correct place and are oriented properly (see picture).
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
