Those Smiths Universal heaters went into everything and work very well. The one in that Gummy add has the provision for 2 rubber boots that you could connect some ducting to and run it to the dash board vents.
GMH had a similar heater called a Nasco and it had 2 little doors to open and shut for heating the footwell or the screen.
Cheers Cobba & Cobbarette
Coopernook, The Centre of our Universe.