I've run chrome Hastings before with no problem, but switched to Speed Pro Ductile Molly. While talking to a friend who Road Races a late model Mustang, he had a bad engine experience similar to yours. Like you he felt his New engine was down on power and did a leak down test that came out only a little better than yours. He took it apart to find the valves were not sealing, so had them regound at a local speed shop. Anyway, he said to try Total Seal Rings because the leakdown is very small. I'll try them when I put my 340 together.