I came up with a S10x25.4 or larger. I limited the allowable deflection to 1/4" and the beam size is governed by deflection requirements, not stress. Regardless, I checked if for a 2g impact on your won ton load and it's O.K. for that. Also, I chose the S shape because trolley wheels are usually canted for these beams. Does this work for you?
Bob G.