Help Choosing Right Material for Halyard Exit Sheaves

[rrranch]

My 4 lower exit boxes are worn out. The boat is a ranger 29 that was set up for some serious racing years ago so it has a lot of stuff on it that is hard to find now. We've been having trouble pulling the sails up and upon checking into it I discovered the mast exit boxes are just worn out. They each have 2 sheaves, top looks like brass and lower looks like aluminum. They are worn flat and no longer turning. I called the manufacturer of them and they no longer make the entire part or replacement sheaves even close to that size. Cutting my mast more to fit new harkens is not an option. It's got enough holes in it already. So I'm stuck making new sheaves. I was considering delrin. I know it is used a lot in this application and I've machines tons of it in my career but what I didn't realize is there are apparently different grades of it. Could anyone help me choose the right one? I didn't plan to put bushings in them or bearings. Delrin is a self lubricating material and should be ok. I will make the exit boxes easier to take apart so future replacement will be a quick task though. I do realize delrin may develop flat spots over time if I leave any of the halyards loaded so I'm making extras. Any advice?