what cam for 340 bored 0.30 over?

If you stay with the 28's, then a higher gear ratio is a prefurred way to go. Just the reverse on a numeriacly lower gear ratio. Like 3.55's, would like a 26 inch tire better. The taller tire would be harder to spin or actually, run 50ft burnouts.

On the Hwy, they will be close in RPM's.