So Paul86S2 where is the best place to buy a flowed/big valve head from?
It all depends what you want Len. As far as I can ascertain you can only really go 0.5mm bigger on the valves without major work.
If you want a decent fast road head, ported and polished with 3 cut valves and seats, new valve guides and seals then I would suggest going on CGTI for the group buy (£350 plus vat), apparently its done by the same guy who does the TSR heads and a few other companies. He also works on a lot of race series and for Radical I believe.
The same guy will do a head to any further spec you want including bigger valves etc.
You do pay your money and take your chance with a lot of work like this. I saw a head recently that cost over £500 and all they had done was some basic port grinding.
Porting seems to be a bit of a weird science, more flow doesn't always equate to more power, you also need to maintain the speed of the mixture through the head.
Paul