351c heads??

i was wonder how much i could pick up a set of 351c heads.... is there a specific year to look out for....my 5.0 has a blown head gasket and im looking for a cheap upgrade... i read in MMFF that they flow 10% less than Edelbrock Performer heads... is there anything else that needs to be changed besides the water jackets.

please any info will help
:dunce: