Got a stock Gen 6 420HP 502 Chev with 8.5:1 compression. Wondering if I could bolt on a set of Mark 4 closed chambered heads to bump up compression thus more horsepower. Got a set of Edelbrock AL open chambered but that won't help anything. I don't think a cam swap would help me either with stock engine. Looking for some cheap horsepower and need some help.