What I found with plastigauge on an old engine is that because the crank and bearings do not wear in a perfectly even pattern, you can get readings that look right but there is great interference. I found that the shop method worked best for me. You will find that the motor will turn quite easily and when you don't have enough clearance, it will make a big difference. Of course, you want to remove the sparkplugs so you are not fighting compression.
