Sorry for not updating this as I've been struck down with a bad cough which kept me off work for most of this week just gone.
I went over to Brian's in the hope of trying to cure the lukewarm heater. We flushed the heater matrix (it was clear) and came to the conclusion that the heater valve was faulty. The fanbelt was retensioned and isn't squealing any more. I'm looking at tuning the carbs so I bought a decent carb balancer from my local Moss. While I was there I bought a 82 deg thermostat to see if that was the problem. Fitting the thermostat was easier than I thought and it has cured the problem. The car warms up quicker getting up to temperature as it should and the heaters are warmer than before. Problem solved!