We photographed our instructions on one of our benches but a customer placed better ones on the forum at www.Stovebolt.com so we used his in the end. Special thanks to Stovebolt.
Remove any screws holding the mounting ring in the housing.
Remove the heater core and mounting ring.
Apply heat near the inlet and outlet tube to de-solder the mounting ring from the heater core.
Pull the ring and heater core from the housing. Desolder and dispose of the 6V Fan
Feed the wires through the side bracket hole.
Drill holes through the mounting ring into the bracket. DO NOT drill into the tank. Place sheet metal screws into the bracket and tighten until the unit is secure in the ring.
Insert the mounting ring into the housing and use sheet metal screws to secure the mounting ring to the housing