Morris Minor Owners Club

That is correct as I said - the Smiths' circular cars had separate rad take-off. You could easily modify the setup though to use the more common radiator and, I daresay boost heat output.

Indeed yes - because the return on the later cars goes straight in to the water pump suction intake !

At the risk of sounding like an anorak, I feel the need to correct something- only early Minor 1000 cars with the round Smiths heater (which was fitted up to the amazing and incredibly rare transitional early 1098 cars...) had the Series II set up with the heater return on the rad- (I guess on a 1958 that could be original). Certainly the later 948 (and 1098) cars with the round heater did not have this set up, but had the extra pipe on the bottom hose, along with the copper pipe. I'll take my anorak off now. BTW, the standard set up on my old Series II was a fantastic heater! I think it's all to do with whether the core is clogged, and how good the pipes and valve are, and of course, the thermostat temp.

I have thought about modifying it to as you say but A - it works and B - I can't afford a new rad for the sake of a better heater..
Mind you, the resto has one I could borrow ;)

Well if it keeps you warm then all is well!

Last winter mine had a mind of its own, sometimes toasty, sometimes stone cold, regardless of distance travelled and engine speed. I'll blast it out and set about modifying the plumbing.