ttmrj;
I've a little gantry too, 1/2t and just over 10' headroom. The first intended use, had to gain every inch possible. I switched lower bolt and link with a shop made bolt, of largest diameter to still fit hook of chain fall. That hook is so close, "repainting will make it hit". That now resides over 16" x 56" lathe, main job is swap lathe chucks and hoisting work pieces.
Tossed around need for a second mobile gantry, and top-running will be preferred, just as yours. Can't see eventual collection of dust being much the issue, even the tapered sections of I-beam collect some, but do have lessened contact.
Still envisioning.