Straight weight SHOULD have lower consumption due to lower volatility, and SAE30 is fine below freezing (not quite sure where the 40F came from, that's wrong).
If you can get it cheap, use it...but el cheapo 20W50, provided actually an API approved oil is fine too...I'd prefer a lighter straight for consumption, but try them.
Back in 1987 (my gap year), I worked in a service station, and the work vehicle was a 1973(?) ford Falcon ute, with the 250 with integral inlet manifold...it was a hideous oil burner. 3-400 miles per litre.
I convinced the boss to try a product on the Shelves, Nulon (Teflon) E10 worn engine treatment. It reduced consumption by easily 75%. It's different to any of the "permament" teflon treatments, is was a clearly visible colloidal looking stuff that had to be replaced each OCI.