340 in a 1966 valiant, remote oil filter woes

The head on this thing is like 1.5", and I did put a 3/4" ratchet on it and made sure it was very snug. I'm sure I can tighten it more, and I may try, but 3/4" ratchet and socket = plenty of leverage :)

I wonder how different the canton is than the moroso. They look very, very similar.
They are.... I think the Canton piece has larger threaded inlet and outlet holes.

If you can turn the bolt any more, that may in turn put a bit more pressure on the filter-plate-to-block gasket. The gaskets may have compressed and 'relaxed' some. The filter plates issues of being too flat and not compressing it gasket to the block, as mentioned above, is a well known issue.