do i use a feeler guage for rocker arms on a 4.2 or just torque down the bolts

 

Torque the hold down to 23-29 ft-lbs (30-40 Nm). That's assuming that the components are in the proper location to begin with. That's for the 4.2.

As for the 4.6 and 5.4 (for anyone who is using the search function) there shouldn't be more than 1/16th" or 1.5mm of travel.