Air Flow Research 227 LT1 performance/racing cylinder heads. About as much done to make these heads as can be to a 23-degree head. Professionally ported by Indy Cylinder Head to flow 326 CFM at .600 on the intakes and 248 at .600 on exhaust. Big improvements on the exhaust side of these heads by the items below that were done and better than a normal competition port job on the intake side. 

Titanium 2.10 intake valves, 11/32 stems, .100 long

Inconel 1.60 exhaust valves, 11/32 stems, .100 long

Copper seats for intake and exhaust

1.580 valve spring pockets

57 cc chambers

Step washers machined into heads for all head bolts to run big block chevy nuts for increased holding/clamping force. 

Stahl header bolt pattern to allow improvements on exhaust flow

Water boss port in-between the center two exhaust valves to solve the heat issue in this head design

O-ringed for copper head gaskets. Have also seen the O-ring setup used with some standard composite head gaskets also to improve cylinder sealing