Hi Denney
Looks like you've got a solid old task force truck to work on. Your GMC engine looks to have been there for a long time, but its not original. I'm sure your trans is a 4 speed, marked as 3 speeds with 'L' for low gear. I think the 40 series is a 1.5 ton, its a great size to haul 2 to 4 ton loads with.
Good luck with your truck and welcome to the Bolt!
James
