Fords L series trucks where available with gas engines and a airbrake  option in the 1970s and 1980s. My dad had a 1979 LNT -800 tandem with a 429 engine not a bad truck but the hydraulic brakes where not as good as our Ford LNT8000 cat engine with air brakes power was about the same.4 mpg versous 6mpg. The funny thing was my dads  truck had a aircompressor on it for the transmission