Aloha TMP,
I have a TF that had an after market heater installed. I'm sorry I don't have pictures and I have removed the heater from the car. I will describe how it was installed hope it may be helpful. I do not think it was dealer installed because the welding, brazing and holes cut in the fire wall were very rough. The heater unit was a small rectangular shaped (about 6 inches wide x 9 inches long and about 6 inches deep) and had an integral fan. It was attached to the under dash bracket and a hole was cut in the under dash shield for the heated air. Hot water supply to the heater was from the rear of the cylinder head. The rear head cover plate was modified by drilling a hole in the center and brazing a a pipe elbow to it. A valve was then attached to regulate hot water flow to control the temperature. Pipe size was selected to match the piping on the heater so one size of heater hose could be used. The return from the heater was made to a pipe nipple welded to the branch pipe between the radiator outlet and water pump intake. Holes in the firewall for the heater hose are made as necessary. The heater fan was connected to an accessory circuit and a small toggle switch can be added or you could use an accessory switch if not already being used.
Safety Fast,
Dave