1953mn,personally I would try and source some good second hand running boards.
I imagine they serve a function other than trapping dirt and rusting!
Or follow Czechman's lead and repair yours,are yours really bad?
Personally speaking, I think leaving them off would be a bad idea,apart from allowing rocks,dirt and other debris up the sides of the bed and rear fenders,it would upset the look/proportions of the truck.JMO.