I can get a set of ported 5.3 heads for $500, this guy I know is porting them and assures me they will flow over 300cfm intake (can take to flow bench), heads come with everything except springs which I will be getting regardless for a cam swap. My question is are they worth it???

 

If they flow that and each port is within 3% or better of each other then sure . CC the ports, if they are not at least 220cc or better then its probably not worth going to the flowbench because odds are not in their favor. Not saying it cant be done, just the odds IMO.