When we had our Dodge, maybe Amsoil was selling synthetic, but plain old Dino Oil was the norm. I think the recommendation then was 10W-30. You live in cool country, so I'd suggest that. The standard oil filter was about a half quart. A longer one was more like one quart and I'd use that if you can find a parts person who understands what you're talking about.
In Florida, the highway patrol cars were Chrysler products and used HD (High Detergent, doesn't mean Heavy Duty) straight 30 weight oil. Our Dodge was a van and we towed a boat on several hundred mile trips. I found it used less HD30 than it used 10W-30 so I used the HD-30, but I don't think you should because that oil will be too thick for starting up on your cold days up there in PA.
I think you have a typo where you wrote "about the 360 like leader size." I don't understand "leader" so if you'll explain or correct that, I may be able to help.