If you are focused on primarily putting the bike back into service and you don’t care about original parts, I agree that there are better and more durable derailleurs that can be found for cheap. Some of the older Suntour derailleurs have proprietary sized pulley wheels that the $10 Shimano wheels won’t fit. (Ironically, those older Suntour pulley wheels would fit on the Simplex RD.) The stock Shimano pulley wheels will not fit the Simplex derailleur, either. That is why the EBay vendor is making bank on the modified Shimano pulleys that DO work on Simplex derailleurs.

I posted the link to the modified pulley wheels with the assumption that the thread creator wanted to preserve the Simplex RD because that was the original equipment. My above post was just to get the thread creator to think twice about sellers who are selling used Simplex pulley wheels because the plastic they were made from are subject to crumbling with age.

I am totally with you on putting age appropriate replacement equipment that works better on a bike and dispensing with purity. My 1971 PX10 is set up with first generation Shimano Dura Ace from 1973 because I place a high priority on it being a reliable bike for my use. I respect restorations that place a high priority on using and preserving original equipment, too. Both goals are legitimate and they lead to different calculations like in this case.