Looking for Compression Tester in Chicago

[lr172]

I will be pulling my cylinders next week to replace some failing piston pin plugs. I ran a compression test today with only fair results. I have a home-made compression tester following the appropriate specs for the air passage. However, I am not sure how much I can trust it. I got the following on a 120 SMOH O-320: 69/72/69/74

There is no additional work to replace the rings with the jugs off, just the cost of the rings. I don't want to go through break-in again if I don't need to, but also don't want to miss the opportunity to make it better while I am in there.

I was hoping to borrow a compression tester from someone willing to loan it in the Chicago area. Please let me know if you have one local and willing to share.

Larry