Open driveline would look like a modern rear end and use a driveshaft. A closed driveline would have a torque tube with a solid moving driveshaft in side. If the rear end truly is from a 41 chevy, and has 6 lug axels, you could tell if it was 1/2 or 3/4 ton by the driveshaft or torque tube. The 1/2 ton would have a torque tube and the 3/4 ton would be open and use a modern driveshaft.
