wich would be the best timing for a 5.0 GT40p heads, shorties, 30lbs injectors 75mm MAF Vortech supercharger (MSD 6AL with boost retarder it came with the vortech)

 

No way to tell without testing / tuning it yourself. It's going to be different from car to car. There are just too many factors involved. Someone could guess and say retard your timing 2 degrees or something but likeI said, maybe that's too much, maybe its not enough.

Some factors... temperature, octane, boost level, engine condition, compression, barometric pressure, A/F ration, current timing level... the list goes on.