I had some SS rocker arm shims made in a .015" thickness, to help in setting up rocker arm side play, when installing rocker spacers. And can also be used to center the rocker adjusters, such as the 911, on the valve tips.
Depending on who's rocker spacers are used, either steel or aluminum, it's often found that they are either too tight or too loose, when trying to set the side play with just the stock .040" shims that come originaly on the rockers.
So if it's too tight pull a .040" shim out and replace it with two .015" shims. Or if it's too loose add a single .015" shim.
Another tip, it doesn't matter which rocker stud you use, the stock 7mm or the heavy duty 8mm rocker stud, which is recommend for dual springs and above spring pressures. You can get extra rocker side play or tighten them up, by moving the rocker stands on the rocker studs before you tighten them down.
My setting procedure is to use a .004 to .005" feeler gauge, place it against the rocker shaft between the rocker spacer & rocker then lightly with your thumb & middle finger hold the rocker stands together enough to keep the feeler gauge in place then snug the nuts down on the rocker stands, then check how loose or tight the feeler gauge is, should you need to loosen or tighten any, you will only need to loosen one rocker stand, for this final adjustment. After you are satisfied with the claarance, torque the stands to the recommended specs.
The price is $12 shipped cont US, for 16 .015 " shims more than enough to do four Type lV rocker shafts.
"EDIT"
For those who would like to get the 911 adjusters perfectly centered on the valve stem, a little extra expense is involved, you can have some material machined off the side of the rocker stands, to allow the rockers to move over to center. This is a extra stept I do for me, but it's really not necessary. Orignaly the the rocker tips were set up off center on the stems, and the keepers butt which allows the stem to rotate in the keepers. This was used to rotate the valves, and the idea was to clean the valve face and seat from rotating the valve. But with HP applicatins now, it is recommended that the keepers have a space between them so the valve can no longer rotate, which keeps the keeper groves on the stem from wearing out. With the 911 adjusters the valves are not going to rotate anyways, and you should have gone to the clearanced keepers.