Does the color of the spark plug electrode in the 60# hole look the same as the others? Check it after a period of idle then again after a period of WOT. I dont think 60# of compression is enough to create combustion. That number can rise as your rpm increases which would give you combustion at high rpm's but not at idle. At minimum I would pull the heads and inspect the cylinders for scoring. If theres noticeable scoring I'd rebuild, If not, replace the gaskets and recheck compression. Maybe its just a blown head gasket.
. Just an opinion from a back yard mechanic.