I also started to clean up the rocker arms and found the rear one to be cracked in the middle, at the middle bolt. My thought is to order a new set of rocker arms and bushing from the filling Station.
Did you mean that the rocker arm shaft is cracked, or the pedestal which supports it, or a rocker arm itself? If it's the rocker arm shaft, buying a new set of two shafts and 12 bushings is the right fix. Normally, one would do that on a rebuild anyway. If it's the pedestal or one of the rocker arms, lots of guys on this site can help with replacements -- just post what you need in the "Parts Wanted" section.
Good luck with your project!
All the Best, Chip