Chevy sb hi-perf heads

[Bt Doctur]

I am trying to identify a set of heads on a 4 bolt 350 motor, rocker shafts are threaded in ,intake: 1- 15/16ths, exaust 1-1/5 ,retainers are flat ,not skirted, casting features found are
PRO
S-RT
casting number c23
Any Ideas????

[waybomb]

Should be a casting number on them somewhere - go here...
http://www.mortec.com/castnum.htm