What can your pocketbook take?
Valve size depends on head size, depends on piston bore.
If you keep the std 69mm crank (big asumption), 90.5mm piston will get you to 1775cc. The valves for that head would be around 40-44intake x 37exh. The 1776 is a decent mid range engine and the heads are where you are going to spend most of your money. Hope this helps.