I have a '50 3600 with a 216 and 4 on the floor. I found a 3/4 ton third member out of a '67-'72. I was able to slide the axles out a couple inches, un-bolt the 4.57 third member, and slip the newer one right in. It gave me a simple upgrade to 4.10 ratio. This set up yields a cruising speed of 50-55 mph, top speed is 62. That is as fast as I'm comfortable traveling on drum brakes.
If you need to know how to determine the ratio of the donor third member there's a thread somewhere regarding it or sometimes the salvage yard has them marked already.
