Hey Truck Guy,
Have them cut for 1.94 intake and 1.60 exhaust valves. Use some Z-28 valve springs if your going to stay around 280 adv. duration on cam. Stay with a dual plane intake and your 283 will do pretty good. Something to think about..... those heads and flat top pistons will require premium + gas! You may want to drop down to a 73cc head to make things more gas friendly
Just my 2 cents,
Alan