when you are referring to a monorail crane are you referring to a single rail I beam supported by frame work?

as it stands you are essentially describing an I beam with a sheave block.

option two is a underslung jib with single suspended I beam-not a good idea due to torsional stress and loading as a jib beam would normally be mounted to a floor base or be mounted directly under a bridge crane trolley to allow for use beyond the confines of the bridge width- so you should go back and examine your intended use. ■

There's one in 3DContent Central website which should download in SATS or IGES formats. Search for hoist. It's not the greatest detail level but what the heck. ■