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Heads for the 60º V-6 come in two flavors; Aluminum and Cast Iron. The Second generation Aluminum heads are far better than their Iron counterparts, utilizing larger diameter splayed valves, and a heart shaped combustion chamber to promote swirl. The Gen 3 heads outflow Gen 2 as well, so for the most flow, you will want to start with these.
Here is what GM has to say about their heads.
Cast Iron Cylinder Head, Part # 14054884
This high-performance cast iron cylinder head is used on High Output transverse-mounted and fuel-injected RWD V6/60 engines. It is machined for 1.72" diameter intake valves and 1.42" exhaust valves. (Standard heads have 1.60" intakes and 1.30" exhausts.) This cylinder head is recommended for off-road V6/60 racing engines.
Aluminum Cylinder Head, Part # 10048649
Production "Generation II" V6/60 transverse mounted engines have aluminum cylinder heads with splayed intake and exhaust valves. This canted valve design enhances cylinder breathing by unshrouding the valves at max lift. The high-velocity intake runners and heart-shaped combustion chambers promote swirl in the cylinders for efficient combustion. Spark plugs are centrally located in the chambers. These heads are machined for 1.72" intake and 1.42" exhaust valves.
Aluminum Cylinder Head, Part # 10218168
These Gen III cylinder heads are used in late model V6/60 engines for improved performance. They feature an increase of .040" in intake valve diameter and a reshaped port for a flow improvement of 16.7% at 0.450" of valve lift. The exhaust port has been reshaped into a "D" port configuration for a flow improvement of 31.7% at 0.450" of valve lift.
See the In Depth area for a guide on head porting.
Bolts/Studs
All part numbers listed below are ARP part numbers. Only the kit numbers are part numbers are from ARP, the rest of the info is from personal experience with the following parts.
Here's is the stud info for the Gen II and Gen III aluminum heads.
8 - Undercut Long studs (11mm x 1.5 & 7/16" - 20) - ATP5.4LU
8 - Undercut Short studs (11mm x 1.5 & 7/16" - 20) - ATP4.650LU
16 - Hex Nuts (7/16" - 20) - APN58 or 12 point nuts (7/16" - 20) - APN12-1
16 - Washers (7/16" ID 13/16 OD) - APW1316N
These studs are under cut, which means that the OD diameter of the shaft is less then the OD of the threads. This actually makes the stud stronger because the OD of the stud is the same the entire length of the stud, instead of being necked down at the threads.
Cast iron head stud info.
Kit with Hex nuts - 233-4003 includes the following
8 - Short stud (11mm x 1.5 & 7/16" - 2) ATP3.75L
8 - Long studs (11mm X 1.5 & 7/16" - 20) - ATP4.65L
16 - Hex Nuts (7/16" - 20) - APN58
16 - Washers (7/16" ID 13/16 OD) - APW1316N
Kit with 12-point nuts - 233-4303 includes the following
8 - Short stud (11mm x 1.5 & 7/16" - 2) ATP3.75L
8 - Long studs (11mm X 1.5 & 7/16" - 20) - ATP4.65L
16 - 12 point nuts (7/16" - 20) - APN12-1
16 - Washers (7/16" ID 13/16 OD) - APW1316N