I got this offof mor-tec's site . All the answers to my questions....If you are thinking about rebuilding a set of old "camelhump" heads or using a set of 1960's or 70's vintage cast iron production heads, check this out first. The '96 and later smallblock "Vortec" 350 cast iron heads are a very hot item. These "L31" heads with casting number 10239906 and 12558062 or PN-12529093 (bare), flow great numbers for a production head, even better than the Phase 2 Bowtie cast iron head, when fitted with 2.02/1.60" valves and bowl ported. The complete heads (PN-12558060) come with 1.94"/1.5" valves and pressed in rocker studs, but can easily be fitted with 2.02"/1.6" valves and screw in studs. Chamber volumes are 64cc and intake port volumes are 170cc. The Vortec heads have raised intake ports and "fast burn" chambers. The heads require the use of narrow body "self-aligning" rocker arms and center bolt valve covers. They will bolt to any Gen.1 block.

The price per pair for new complete Vortec "L31" 350 SBC heads (PN-12558060) is about $485.00 (as of 11/1/03), with 1.94"/1.5" valves, springs and retainers from GM/Performance Parts. You can then use the valve sizes you want to use and drill and tap for screw in studs. However, the intake manifold bolt holes are in different locations than previous Gen.1 heads. Only four intake bolts are used on each side to fit the "Vortec" style intake, instead of the usual six on each side. The correct Vortec intake manifold bolts are found under PN-12550027. Use Vortec intake gasket PN-12529094. The stock Vortec L31 valve springs are good for lifts up to .475"-.480" maximum. If you use a cam with more lift you'll need to change the springs and have the valve guides machined down to clear seals and retainers.

You can try to redrill and tap the heads to fit the older style Gen.1 intakes, but why bother. Edelbrock has aluminum two and four barrel "Vortec" style intakes out that have the correct bolt hole positions. Edelbrock PN-7116 is their "Performer RPM", dual plane, high rise intake for the "Vortec" heads, while Edelbrock PN-2116 is their "Performer" street dual plane for 4-barrels. They also have two "Vortec" versions of the new "Super Victor" aluminum, high rise, open plenum race manifolds. PN-2912 is for 2-barrel restricted class racers and PN-2913 fits a 4-barrel intake to the "Vortec" RPO "L-31" heads. Vortec style intakes are also available for TBI and TPI setups.

GM/Performance Parts has a dual plane aluminum four barrel intake that is PN-12366573 and fits the unique Vortec intake manifold bolt pattern. GM also has a aluminum open plenum high rise (PN-12496822) intake for the Vortec L31 heads.