It will be a very large task to try to retrofit a system onto an older combine from a newer one. The electrical will be very involved, diodes, relays, microswitches, sensing pads on the header, extra hydraulics installed for the lateral tilt system. Check for a jobber system or something like "Sensetek", which is a jobber that builds sensors to mount on the header to keep it at a desired height from the ground. Maybe a Honeybe header would work for you, they can be laid on the ground for harvesting.