yes, many discussions - some think the in cab tank is a danger, but nobody has ever been able to find a report of the tank exploding or being the cause of a fire in a wreck - most leave'em there, cuz it's actually the most protected area in a wreck, but there's any number of ways to put a tank under neath where it can be smucked proper if you get rear-ended
also been some who can't be bothered to get their tanks and fillers in good enuff shape to avoid the gas smell in the cab and think it's easier to install a tank underneath, where they can't smell the leaks
and the pre-1960 trucks didn't use the "C" or "K", just the series numbers like 3100
Bill