i rebuilt my 89 f150 302 it ran fine before i took it apart. when i put the motor back together all the rocker arms tighten down fine. just some are loose where they meet the push rod like as if they have worn down but they were fine before i took them off is then any order they should be out back on i see letters stamped on the rocker arms
in this case your best bet is to buy new pushrods and rocker arms. otherwise you will eat the cam. just curious, have you turned the motor over by hand to make sure its just not the position of the lifters that are making some more loose then others? so in other words if the loosness changes to different set of rockers as you rotate the crank then everything is probably fine.
Lets see what others say also.
ya i have ran the motor a couple of time and drove it to my new house so probaly about 30-40 miles. not all the rocker arms are loose i have move one that was loose and it tighten up a bit while the other one i traded it for loosened up so not sure i have measured a gap of .050 between rocker arm and pushrod on one of them