What you ask for doesn't exist. There are a whole host of reasons why it can't be done easily like it can on a model a. That's why there is no kit. I don't want to rain on your parade, but even if the pumpkin bolt pattern is the same as something later (possible), there are other things that deserve more of your attention. I'll start with two. I would encourage you to crawl under your car and imagine how you would deal with these 2 things, and whatever other changes you would have to make as a a result of them. That would be a good start toward understanding exactly what you are up against.
Firstly, the rear axle is not solidly attached to the rear springs on old Chevrolets. It is sort of like a bearing or hinge. When a wheel drives the car, the reaction force is taken by the torque tube, which acts as a giant lever. If the torque tube were not there, the axle would wind up and rip the driveshaft out. You would have to change the way the axle mounts to the springs from hinged to a solid mounting. That makes using an original housing less attractive. Also, the springs will now be taking the torque reaction force where they didn't before. They were not made for it. On 1950s era Chevrolets, some people have got away using the originals. I wouldn't count on it. There is a good possibility you might need custom springs.
Secondly, the torque tube in a Chevrolet runs dead center in the car. On an early car like this, the torque tube comes out of the center of the pumpkin. A hypoid axle has the torque tube or dirveline coming out down and toward the right. Chevrolet kept the driveline dead center when they switched to hypoid in 1937 (cars) and 1940 (1/2 ton). This means in the new designs that the "bulge" in the axle housing that the pumpkin bolts to, and the pumpkin itself had to move left to keep the driveline centered. Now the axle shafts are 2 different lengths, negating any idea that your axle shafts would work in a later housing, even if the splines happened to fit. If you got a newer open-driveline pumpkin to fit in the old housing, the driveline connection will be down and to the right. The driveline will be running skewed in the car. That isn't necessarily a dealbreaker, as long as it doesn't hit anything. I am not sure about 1931, but on a lot of Chevrolets it would hit the frame.
In my opinion, if you must do this, you would be lots of money, time, and frustration ahead to use a whole later axle, and figure out what it would take (probably custom axle shafts and some fabrication) to get your wheels and brakes attached to the newer axle. Good luck on your Great Race campaign!
Last edited by bloo; 06/27/22 11:14 PM.