I referred to the Purple Sage and Stan Weiss sites for head flow figures on these heads. This is stock flow, unported, so if your heads have been ported (I'm sure that was in the plans of whomever did the other work, but don't know if they got around to it) they will flow better than these figures. But you have to consider, if they have been ported, are they eggshell thin in some areas and subject to cracking as soon as you add some heat? That's the other thing I might do if I had glommed onto some unknown heads, disassemble and magnaflux for cracks. Cheap money to pay for finding out ahead of time.
Stock, the intake ports are 151 cc's, exhaust 59 cc's. Intake/exhaust flow at given valve lifts is as follows:
0.100" 70 58
0.200" 125 108
0.300" 175 135
0.400" 204 141
0.500" 205 142
In comparison, the L31 Vortec heads, a much-sought-after production casting, casting numbers 12558062 and 10239906 show published flows as follows:
0.100" 70 48
0.200" 139 101
0.300" 190 129
0.400" 227 140
0.500" 239 147
Now, you have to take published flow figures with a grain of salt. The only way you will know definitively is to flow each head you are considering on your own flow bench under the same conditions (temperature, humidity, bore pipe size, valve stem diameter in the port, depression of water on the manometer, etc., etc.)
Bottom line: If they're not cracked, they should make some decent daily driver horsepower.
