It's been a long time since I owned a GTV1) Can you remind me what the service intervals are? Is it a 6K service?
I only use mine about 3-5K miles/year, but it gets an annual service - and regular oil checks etc.
2) How much is a water pump?
3) In terms of modern tyres, what works well for the GTV6's set-up on factory standard GTV6 alloys? My personal preference is a tyre that's exceptional in the wet, while excellent in the dry (what I'm saying is that I don't want a brilliant dry tyre that's only so-so in the wet. It gets very slippery round here in the autumn and early winter, hence my preference)
I use Yoko A539s which are no longer made, unfortunately. They're good in the wet, though I don't tend to go out too much in the rain, and very good in the dry. Something similar like Toyo Proxes should be OK. Goodyear Eagle F1s are great in the wet, but I don't have any experince of them on the GTV6.
4) What tax category does the V6 2.5 fall into; so how much would the UK road tax cost?
About £180 per year, IIRC.
5) Is it easier now to upgrade the headlights (they're rubbish, usually). I think i saw an ad for a company that offers 21st century headlight performance for older cars. I hope they do an upgrade for the Alfetta.
Alex can supply you with new-style bulbs which are a direct replacement for the originals and much brighter. Headlamp units are very hard to come by now.
6) The RS (?) suspension upgrade. How much is it, is it worth it, and does it compromise the ride at all? Should it affect which tyres I choose?
It's the best I've driven and doesn't compromise the ride too much, IMHO. It is a bit twitchier at the back than most other kits, but that's the way Ron (Simons) likes it. Can't remember the cost, but it's at least 50% more expensive that e.g. a Harvey Bailey kit and is worth it IMHO.