Stock heads and rockers?
same one keeps coming apart, or more than one or ??
when it is all toghether, does it run OK and for how long till things come unglued? My first thought is that the rockers are not tight - or are missing parts (the little ball type thing) Are the push rods strait? roll them on a pice of house window glass (cause it is flat) to check for bent rods.

By wear in push rod guide of head - do you mean the large-ish hole, intake side, that the push rod passes up through from the lifters to the rockers? The push rods shold not touch anything on the way up at any time.