Workshop Crane Beam Size

Folks can someone please suggest a size for a steel I/H beam that will be asked to carry a max load on center of 3 ton with a span of 20ft. Both ends will be secured. Used to carry a chain host rated at 2.5ton. I don,t mind over engineering it but am looking a ball park figure, from someone who has one in use maybe. I am also looking to design a moving gantry system using railway rails as the carriers the length of the workshop (45ft) each is well supported along the length should be a very solid support rail, has anyone ever used railway tracks? I can get these for free as it is old bull-nose pattern now no longer used and scrap value only. George