5000 miles? That's neat. Just my take, Tyler, but I'd use 30 weight Valvoline VR1 in the summer and in the winter maybe 20-50 Valvoline VR-1. I don't believe I'd go with the synthetic stuff. As others have said, I don't think the design will be quite compatible. Good luck!

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end