1986 GMC

Hi all! New Guy here!! I bought a 1986 GMC C7000 single axle dump last fall from a guy I work with. I drove the truck for him a few years ago so I have some knowledge of the truck. It has been sitting for a few years so I plan on doing some work to it. The Vin says it has a 427 BBC engine in it. Its back by a 5 speed transmission and a 2 speed rear axle and air brakes. The odometer says 81,096. My question is what oil should I run in the engine? I was thinking about 15w40 but not sure. I am...

1986 GMC

1986 GMC