temp gauge issue has been resolved!
To buy the original Volvo gauges and mounting kit in Oz was going to cost just over $350 and so I was looking for an alternative. The coolant hose that goes into the heat exchanger
has a 16mm internal diameter and I found a hose insert with temperature sensor mounted for $29 (http://www.trailtech.net/7500-3041.html
and it would couple with any standard gauge for a cost of approx $70 per side so about $140 total for the 2 engines and still a less than optimum installation
Then, and quite by chance, I found a fantastic website in the UK
Coastal Rides - Discounted Boat Parts & Marine Engines Sterndrives Pumps & Motors
They had the Volvo gauges (part number 874904 for the black face) for only GBP 15 each!! I had 2 of them sent to me and they were delivered within 7 days for a total cost of GBP 63 ... about Aus$100.(postage was more than the cost of the gauges!) Picked up 2 mounting kits locally for $27 (part number 874709).
Two holes in the dash, plug
them in and hey presto ... coolant gauges! Total cost about $130 .... I couldn't be happier!
A word of warning ... before you drill any holes be aware that the gauge connecting harness is relatively short which means the coolant gauge can't be positioned very far from the tacho.
Thank you to all that replied to my questions regarding alternate strategies.