You may think the same thing I thought when I found these heads. GM never made a set of cast iron 18 degree heads !! BUT THEY DID, one (1) set !!
These heads have been CNC ported and polished.1.150 tit. intakes, 1.6 tit. exhaust.CV Products tit. retainers and keepers. Don't remember the exact flow numbers, but it was way over 300 CFM.
Have Jessl 1.7 intake and 1.6 ex rockers. I had the intake made in a NASCAR shop in N.C.They took a 23 Degree 103 intake and an 18 degree intake and made a high flowing intake.
Also have a set of duel tapered pushrods made for high RPM that won't flex.I had these on a very short stroke 359 CU. IN. truck pull engine that broke a rod. It junked the short block. The heads have a bent in. and ex. valve.
I had over $8000.00 in the heads.
ALSO the little 359 CU. IN. made 780 HP.@ 10000 RPM.
All of the above goes with the heads !!