The Suntour Winner is not going to index with Shimano and depending on which generation it is, may not index with suntour stuff. Suntour winners are great freewheels but suntour was late to the indexing game. One of my better scores was buying all the winner freewheels from a bike shop. I'm sitting on a lot of 5 and 6 speed freewheels. Ideally you would pick up a 6 speed Shimano freewheel. They were beautiful freewheels and indexed nicely. I think I have one or two in the old parts box but they are probably 13-21. IRD would be a very good choice and they are not bad at $40 or so online.