A good service prep with valve job is needed on almost every aftermarket cylinder head. I never install any cylinder head OOTB. They need to be disassembled, inspected, corrected and cleaned. I have found Edelbrock heads with out-of-round valves and seats, guide clearance too tight and bad rocker shaft heli coils. The bad heli coils are generally on the right hand side of the head and need to be tapped or replaced so that the bolts will screw in by hand.