Curious about Variable rate but we are running older equipment. We have a Flexicoil 3450 cart that is variable rate, a JD 1900 Cart that is Variable rate, and a Case 955 planter. Can the monitors/controllers be upgraded on the carts to do "today's" variable rate? also, is there electric or hydraulic drive available for the 955 planter or are we just to old to try this? Thanks in advance.