Bob Johnson's comments, as coordinator of the archives of the PRRT&HS:
1 - As built in 1-1929 to 4-1929 the cars had no side ladders and had the end ladders on the right side of the ends as you stand facing the end of the car. The side sill steps at the ends were a two-step style.
2 - About 1932 some, but not all, R50B cars began to receive freight car safety appliances. This added side ladders, changed the side sill steps to a single-step type, moved the end ladders to the left side, moved the brake wheel, added a brake platform, added a platform above the end ladders, and modified many handholds.
3 - On 4-3-1940 a second handhold was added on the left end of the sides of R50B cars with freight car safety appliances, but not to cars that kept the original configuration.
4 - On 12-18-1942 the end details described in #2 above were made standard for all R50B cars. This made a new variation with full freight car safety appliances on the ends, but no side ladders. I haven't seen any photos of this variation.
5 - Beginning in 1952 the running boards and side ladders were removed.