Yes, very common in the larger trucks.
Someone had put one in my 52 1 ton, and I have a spare, honestly I can't say I remember seeing an SM420 without a parking brake, but then again I don't look under the baby trucks much...
Post a wanted add, and you'll have one pretty quick.
You may need to swap a number of parts on the back of the transmission, probably simplest to just swap the whole transmission, as they are usually pretty cheap.
Grigg
