340 in a 1966 valiant, remote oil filter woes

Is this the part you are using? Moroso 23682, If so It does use the plate.

View attachment 1715242315
That is the part.

With the massive bolt head, that I'm sure most people might only have a large crescent or use a pipe wrench on.

Sadly for me there's no way to get any tools on that thing while the header is in place in my car.

I do love these headers, but good god damn they are a labor of love.