Oh. I thought it was a sm420. And yep it's original what ever it is. The same bonehead that left the engine open to fill up with water and lock up let water get in the trans. The forward gears are rusted up as well asthe main shaft and won't budge. Thought upgrading would be easier and better than repairing. Found a sm420 from a 53 gmc but discovered it won't bolt to my bell housing. Have the entire gmc 1 1/2 ton chassis with open driveline and 2 speed axle.