Thanks for your replies guys.
Heater Core is approx $450.00
I'll take your advice Snoopy and have the used core i purchased ($100.00) tested before I start. It looks to be in really good condition though. I tried Sandwood Trading, they don't have them for the early models V40/S40s.
Bear, I searched the UK forums
https://www.volvoforums.org.uk S40 / V40 '96-'04 General section.
Couldn't find anything re Heater core for v40/s40. Do you remember where you saw the write up with pics? That would be a really handy thing to have.
Cheers
Jagger