I think the advice above is correct regarding having a shop make up the correct length for your drive shaft swap project. Yes they were a factory option as I have a 1959 3100 with SM420 driving a Spicer 45 rear axle. I cannot measure it now as the truck is back in storage until spring but if you can get your parts in place and get your truck to a drive shaft shop that would not seem a difficult job for them. Yes mine is a one piece propeller shaft with the splined slip joint,
