Yeah ian16th that certainly was a typo on my part!
It is often believed that the Vipers were originally part of Ph3, in fact some MK3's were updated to Ph3 without Vipers. They were later returned for the fit to be installed. The Viper was a separate add-on that eventually got rolled into the Ph3 programme.
Later mods to the Viper throttle system replaced the two switch idle/max with an inching system that allowed any rpm to be selected. The real issue was the small amount of oil that was carried.
pm575