Well I'm sure you could pick up some power with a different cam but if you are using shaft rockers there is a limit to how big you can go before you'll have problems. Do you know what valve springs are in the heads and what the installed height is? If the heads came from Indy fully assembled then the parts might not be in the best shape. Indy sends stuff out the door assembled for shipping rather than assembled for racing.

Do you know what your valve to piston is with the existing cam? If you know that number and the installed height on the springs then you could get really close with the next cam choice.

Personally I don't think you need to change the cam much. Maybe put the 1.60 rockers on there and double check valve to piston and spring clearance. If the 1.60 rocker fit and work then try it at the track and see what it does. Since you already have the parts that will give you another clue.