Thanks guys for the responses.
Re thermostat - when stationary she gets up to 90c and the fans cut in slow then high speed, it's when rolling that the running temp drops to 80c, my 166 always maintained 90c even in winter, so I guess I'm answering my own question!
Thanks for the tip re the fuel release, will dig around the boot liner panels and try to fix or plan for the replacement :-)
No idea about MPG, never bother to calculate. Was all a bit unreal as on the way out we were in convoy with a friends 78 Renault 16TX with a newly rebuilt engine so did a steady 65!! But happy to report that at speed a 3.0 GTV is very economical. Overall she was pretty good even at a 85mph + cruise, a great GT car and a joy thru the twisty bits. I reckon I got thru 2.5 tankfuls max. Worth every penny of unleaded. Go take that busso out for a real adventure :-)