I installed an Espar Airtronic Diesel heater in my '73 710M. There are a lot of these units out there because they are very common in the trucking industry. It is very easy to find a used one on eBay.
I mounted it behind the driver's seat and for a fuel supply I tapped a hole in the top of the jerry can on the left side of the vehicle with a dip tube going into the can. I just fill that can with diesel and I am good to go.