How badly marked is the bore of the rocker arm?
The 906/RSR/935 Rocker Arms didn't have bushes and ran on a specially treated rocker shaft that had a coating applied.
We have re-manufactured this type of shaft with a hard layer (1000 HV). The technique we have used also produces and oleophilic surface so holds an oil film.
If you can lightly hone the bore of the arm and keep the diameter within spec these shafts may help.