If you are using a stock casting head a .310" lift cam with 1.25 rockers is the max.
The reason being that with the proper tension valve springs you will be extremely close to coil bind with that combination.
With a well designed billet head you can use a bigger cam and not have coil bind but you will need to pay close attention to all the valve train components. A .310 or .315" lift cam (close to .400" lift at the valve) will work well on my billet heads, make good power and provide reasonable life.