Welcome to the 'Bolt!
I am 99% sure that you will have to swap out the entire rear end to put an open driveshaft tranny on that.
They did make a 4 speed that fits the torque tube on the half tons. Check the swapmeet section. There are a lot of guys who rod and they might have a 4 speed that'll work for you. If there's not one posted anywhere, post a request in "Parts Wanted". Someone is probably looking to clear out some garage space.
Another option: A 1/2 ton rear from a later model should work. I think that the axle off of a 55.2-59 will be what you'd need.
