The lift is an easy fix later if you cut the valve pockets now for more lift and the required valve clearance at that lift. The aftermarket now can supply higher ratio rockers for almost any pushrod engine. Besides valve pockets the pushrod to head clearance should be checked. The length from the rocker pivot center to the valve center does not change. The distance from the rocker pivot to the pushrod cup center is shortened which tends to bring the pushrod closer to the cylinder head. Normally a bit of grinding can provide the necessary clearance.
With the rockers you have now the pushrod to the cylinder head can be measured. The rocker dimensions can be measured and the dimension change on the pushrod side can be calculated. Any required grinding can be done prior to final head installation while the heads are away from the shortblock and can be cleaned of grinding debris. Later the rockers can be replaced to get that lift you wanted or close to it. Way less of a job than replacing the cam.
On my 289 I want around 0.500" lift. To get that with a cam I have I am going to use 1.7:1 Scorpion roller rockers. For stability I am installing screwin 7/16" rocker studs instead of 3/8" studs. For my mild cam I should not need a girdle.
