Actually, the U50C re-used 3 axle trucks off U.P. turbines, as the " C " designation implies. It was the original U50 that had a B+B - B+B wheel arrangement. GE had hopes that the use of a 3-axle truck might make the U-50C more appealing to U.S. Railroads; however it was still too much locomotive for everyone but U.P.
ALCo's version of the double - diesel, the C-855, used the same B+B - B+B wheel arrangement. In this case, the " C " stood for Century, not the use of a 3-axle truck. I recall also a few electrics with the B+B - B+B wheel arrangement ???