What is the difference between the sm465 and the ch465?

[72timemachine]

I've done some research, however there seems to be little to no difference from what people in some of the forums are saying about the difference in these two transmissions.

The one I have came out of a 1969 c60 dump truck, I believe it was a 2 1/2 ton. It looked like it had a 2 speed rear end, just massive. The engine was a 366 ci mated to the ch465.

Now I am no way an expert on this but is this a 4 speed manual transmission? I believe it has the 13" clutch, very odd looking too. The stick shift lever is straight up and down, no curves in it at all. Shift nob was missing. It has a pto with a small drive shaft attached to work the dump bed hydraulics. It also has the emergency brake drum attached to the tail shaft. I swear this thing weighs almost as much as a small block Chevy engine. It took 3 guys to pick it up and throw it in my truck.

There has to be some difference, otherwise, why would GM bother. Does "ch" designate GMC or something, whereas "sm" designates Chevrolet?

Not kidding, I see some of these sell online from $100 to $1700 and I have no idea why the large spread in the pricing.

Thanks for any help.