Looks like I was wrong the track type. There were some SP with the old style track. Somewhere there are an modernization of the M50 SP. It seems upgrades occurred on the early 70's. The filters on the superstructure had been removed during upgrade. The gas engine was replaced with a diesel This version would be for the six-day war. The HVSS would be for Yom Kippour.. OOPS my mistake.