According to Sam Weiss' flow sheets
, the L30 305 Vortec head flow respectably even unported: 221 cfm int./163 cfm exh. @ 0.500" lift/28" water. Better than all but one professionally
Needs springs/retainers, a Vortec intake, center bolt valve covers, and either self aligning rockers or adding screw-in studs and guide plates to use standard rockers.