My Wd carries very little oil pressure (needle just barely into the normal range) when it is warmed up, and has done so for as long as I can remember (20 years). Has the correct filter.
Another option you may want to consider is that Allis used Brass shims in the rod caps and main bearing caps of the crank. These shims can be removed to decrease clearance if yours are excessively worn. Use plastiguage to recheck clearance. I forget what the factory specs are, but you can find them in a book.
I've come to accept the low oil pressure as part of the "nature of the beast".
Good Luck! Enjoy that WD!