how do you sleeve pshrod holes?

Sleeving the pushrod holes in the 587 head will yield no significant change until the most extreme upper lifts and flows. By this I mean, until you are in the 280-300 cfm range and .600"-.700" lifts in those heads, you will reap no benefit. Then you might see 4-5 cfm gain if you are fortunate.

The pushrod pinch area of the 587 head, without sleeving it, is capable of 292 & 298 cfm at .600" & .700" lift.

A-n-y-w-a-y. You can use a 9/16" X .014" wall brass tubing, ream the pushrod hole to 9/16", coat the tube with Loctite Sleeve Retainer and press the tubing into the reamed hole.