The baby turbines, as they were called, would probably not be found running with the U50's. The 4500hp turbines, both slab side & veranda, were in service from 52-64. The U50 service life was from 63-77. While there is one year of overlap in the service lives of the two classes, it's not too likely you would have found them together. It was typical for Locos that were at the end of their service lives to be stored, in some cases years, before they were actually scrapped or sold and removed from the company books. Also, if you recall your UP history, the U50's rode on the trucks and span bolsters of the traded in turbines. One of the favorite diesel partners for the 4500hp turbines were the GP-9's. A common partner for the U50's were the DD35's, which hopefully Athearn will provide for us.
With all that being said, anything is possible. As they say, there is a prototype for everything. If you want to run them together, I promise I won't tell anybody.