I was told before that for quince jelly and quince paste one needed wild quinces and not cultivated ones which have much less pectin in. (I am talking on overseas knowledge, they have lots of wild quince trees in South west France)
Also, how my family do it (it may not be any use to you but I'll say it anyway) is they boil the quince in water, then strain the cooked quince in a cloth over a pan, keep the water to make quince jelly (adding sugar and pectin if necessary) and then the heavy quince solid they put in a pan with sugar to make like a jam, which when cooked (I don't know how long but could find out if anyone is interested) they put in low dishes and leave that to dry several weeks in a cool room. It is usually very set. My aunt is very good on quince paste if anyone wants to know. With pleasure I will ask.
Good luck!