Gee, Jack! Long time no see!!
As far as the heater goes, the original unit should about cook you out of the car after a short while. If it isn't working well, there's got to be a restriction, either in the core or the control valve. Another reason could be the seals around the box itself, the "fresh air vent" seal, door seals, etc. Every MGB I've ever had would get warm enough in the cab to warrant dialing the valve back a bit after a short time. And that was in the Pennsylvania and Virginia winters.