I found out that if I could just add the TH400 yoke to the Studebaker truck drive shaft I could use the factory shaft with the 425 Caddy swap into the 59 truck. The problem was that one half of the U joint was mechanics style, the other was the larger Saginaw cup. All the "conversion joints" I could find were Saginaw to Spicer cup (wrong clip style), but my local auto parts guy came to the rescue. He used a micrometer to measure the diameter of the Studebaker U joint cross that fits in the cup and found a larger Saginaw cup that size. By taking two new U joints and swapping cups I now have a brand new GM to Studebaker truck joint.