I own a welding and fab shop. I have some left over steel, and thinking of a gantry to help in loading my shear and power rolls. Span needs to be 14 feet. I have 40 feet of s7x 15.3, also 4" schedule 40 for the uprights, and some 6x4x1/4 tube for the bases. Was thinking of 3" channel for the upright gussets. Mostly it'll be used for 72x144 sheets of 10 gage, but would like to know the realistic capacity. Anyone know? Also would like a recommendation on 6 or 8" casters.