Many many people on the vintage Mustang forum are using Mobil 1 15w-50 on their vintage engines, worn or fresh. It’s not expensive, easy to find at any Walmart, and recommend by Mobil for our vintage engines. It has great wear protection as well. I’ve been using it for 20+ years on many different cars of mine, and customers cars too. After 85,000 miles on one Hi-Po 289 I checked the main bearing clearance when the oil pan was off to switch to a different pan. No measurable wear.