well today finally removed the heater unit from under the dash...no wonder it does not work....rusted to hell and back, and all the old foam has collapsed/disintegrated so is knackered. A while ago I bought a new matrix from RIMMER Brothers, but of course now I find it is for the later Metre/Rover 100 and does not fit.
So, decided to visit my favourite car builders emporium - www.cbsonline.co.uk - and have bought one of their small re-circulating heater units (aka fug stirrer), but will continue to use the original engine bay fresh air intake and fan unit to a couple of vents on the dashboard !!
Got some manufacturing to do to make this work...photos to follow as work progresses !
Dave