Hi,
I don‘t know if its allways the same, but I‘ve the same engine-transmission combination in my 78 truck.
I bought a LUK 04049 Clutch set and it is an 11 Clutch.
If it‘s allways this size in a normal truck and when it needs a 12 or a 10 i can‘t exactly say, but a rockauto the 12 and 10 clutches where offered for Big Ten or Heavy Duty.
Regards
Chris