Were the rockers getting oil up there while you were running it? I purchased a car with a 225 slant six that had sat for almost 35 years and at first it ran smooth but kept getting worse and running more ragged. When I pulled the valve cover I found that the intake valve on cylinders 3, 4, and 5 were stuck due to lack of oiling and the number 5 pushrod was bent. The other two had jumped out from under the rocker arms. First I put some oil on the valve stems and tapped them with a hammer to get them unstuck. I pulled the rocker shaft and found the passage in the head from the rear head bolt hole to the rocker shaft hold down bolt hole was full of gunk. I had to take the rear head bolt out and clean the passage to the rear rocker shaft bolt. After I did that, it ran smooth and oil came out the top and ends of the rockers as it should. Hopefully the shop made sure that passage is clean.