I fitted one of those kenlowe heaters to an Austin Montego, in the late 80's. It worked very well but was prone to sticking. At the time Kenlowe advised against anything but plain fresh antifreeze mixture, regularly changed, otherwise pump sticking was inevitable.
If anyone remembers the Montego then lack of heat from the heater was quite normal! Apart from that it was the worst car, for reliability, that I've ever had anyway.
I've been tempted to fit one to the terrano but bad memories (& the expense!) stops me every time LOL. I'll stick to blanking off the rad.....it's less hassle LOL.