I have the Walthers Cornerstone Sanding Towers Kit
The have different towers for the steamers and diesels and show a facility with both
Diesel Tower is taller etc
Is there a reason for the difference and why couldn’t the steamer be used for the diesel and vice versa ?
The sand domes on steam engines were nearly always on top of the boiler. The sand filler on most diesel engines is on the nose and is at a lower location than on a steam engine.
I don’t know the kits, but most likely the difference is merely one of design evolution. Much the same as with the gas pumps where you fill up your automobile - the design has changed greatly over the years from early hand-pumped versions where the jockey first filled a graduated glass globe to today’s semi-automated pumps. Diesels could quite happily use sand towers originally designed for steam locomotives, and vice-versa.
The sand filler hatch location on a 1st generation diesel varied, but a not uncommon place was on top at the end of each hood. I believe each truck was supplied from its own sand source so shop forces had to fill both ends. (Although at least one Canadian branch line design had the sand boxes mounted on the truck sideframes themselves.)
Once steam was gone, the work flow in an engine facility was vastly changed. It was often better to build a new, modern, sanding facility by the fuel racks and demolish the old one with the rest of the obsolete plant - coaling tower, ash pit, etc.
John