The US Forest Service adopted enclosed cabs long before they were required. The Model 51 and 60 were introduced in the late 60s to replace designs with open crew benches behind the cab.
1968 Ford F700 Model 51
96 gpm aux pump
300 gallon tank
Photo credit USFS Archives
1968 Ford F700 Model 51
96 gpm aux pump
300 gallon tank
Photo credit USFS Archives
Aaron Woods