if you're getting quotes for a "classic" policy then no claims doesn't apply as far as I'm aware, there's no discount for it and you don't build up any. So you might want to bear that in mind, if you at some point buy a newer car and have to go on a non-classic policy you may have no NCB built up, check with these companies you're getting quotes from.
Some of them are arsey about mods too I thought.