Imperial Services makes the reducers any size you want.They arent cheap though.I have 3.91s in the 65 and my speedo is only about 10 % off.I believe I have an old Mopar reducer in the other garage.Bought it and never installed it.Ill have to find it and see if it is as Im going back to 4.88s or 4.56 and with those the speedo is way off.Oh I have seen some list the newer gears as fitting the 65 backs.They dont.Rocky