Hi Jack . . .
The car rearends are different than those found in the trucks. With the trucks (from what I've heard) any ratio can be bolted into any rear-end. Not so with the cars.
California Bill Fisher's book documents the ratios available to those of us still running cars with enclosed torque tube drivelines:
Your '50 with a 216 has a 4.11 unless the original owner ordered it with a 3.73. If you can find a 41-11 ring and pinion set you can bolt in a 3.73.
My '49 also has the 4.11. I am going to a 3.55 ratio this spring. California Bill cautions in his book "1950-51 Power Glide Models are equipped with 3.55:1 ratio gears. In order to install this gear set in 1940-51 rear ends, it is necessary to change the case to which the ring is bolted. Part number for this differential case is 3691463, and it is stamped 593009. Under no circumstances should this gear ratio be installed without changing the case!"
For this reason I went shopping for a donor rearend:
This one is out of a '52 Power Glide car which is confirmed by verifying the stampings that California Bill lists:
With the 'case' that Bill is talking about "the ring gear being bolted to" pictured here:
My plan is to take the best parts from the donor rearend and the rearend that is on the car during the rebuild . . .
Hope this helps.
stock49