I think it is common for the big trucks to be seen with 216s. While originally they may have had the low-pressure 235s - I'm not certain whether they were standard or just an option, but Tim is probably right - the biggest weakness of the Chevy six was the thin casting, which led to the blocks cracking in the water jacket. My fire truck had this happen, and the department repowered it with a 216, because . . . well, 216s are a dime a dozen! They could get one at the local salvage yard, and it only lacked like 7 horsepower compared to the 235 (I know, I know . . .it's the torque that matters! Still . . . ).
Anyway, there's no doubt that for the big trucks, the 216 is underpowered. However, the original 235 was ALSO underpowered, and it was the biggest engine they had. There's a reason they come with that stump-puller 1st gear! That being said, I run my truck occasionally with it's full complement of equipment and 500 gallons of water. It's slow, but it goes! Without the water, I find it satisfactory, and usually enjoyable. Someday, I'll find the low-pressure 235 to rebuild and put in. Someday . . .
-Michael
