Like Andy said, it depends on cam lobe profile, and other factors.

There are a lot of trade-offs when working with the original block and head dimensions.
Most of the high lift cams are designed for higher ratio rocker arms, because the cams lobe lift (lobe height) has to fit through the cam tunnel, and you can only reduce the base circle of the cam so much before the cam torsional twist throws the other cylinders timing off (although it can be compensated for to a point.)

For the most part, going from 1.5:1 to a 1.6:1 is pretty easy, and general work with no to little changes. Need to check pushrod clearance around the heads, valve spring coil bind, and piston to valve clearance. This assumes you are using pushrods of the correct length and strength (Thickness, material, etc.)

With the rockers themselves, I think around 1.7:1 ratio is about it using the factory rocker shaft size and location.
If you want higher ratio, and valve lifts of 0.800+, you should goto a paired shaft rocker system that re-locates the rocker shaft location. Not to mention the valve spring pressures with these aggressive cams will be hard to retain (keep bolted to the head) a stock rocker shaft system with the five hold down bolts.