401 heater modification

[p5b401]

Investigation of a pax side leak from the heater found it to be a perished hose elbow - of which there were four.
The 401 spares book did not show my assembly and further investigation suggested that it was a modification.
The original heater matrix was in place but a further two heater matrix have been fitted and plumbed in serial fashion as per photo (most linking pipes and hoses removed for clarification).
I pressure tested all three and there were all good but plainly this would potentially pump out a lot of heat (with a window open or a cabin exhaust air vent fitted).
The car originated in NSW but is now in WA and with no experience of driving this car in a really cold environment, I don't know if the normal heater configuration need this kind of boost
Is this a Bristol mod or someone that got really cold?
Thoughts appreciated
John