Why is this 360 pinging

Ok got a buddy that does not know two much when it comes to tuning.he has a dodge truck with a rebuilt 360 with the KB 107 pistons,stock intake,stock heads,stock exhaust manifolds,and the edelbrock carb,727 tranny with 323 gear,cam he has forgotten what the spects are.He has had pinging from day one he runs 91 octane gas.So he turns to me for help,goes and gets a new dizzy with no vacuum can this has been re-curved.I installed it for him ,set is timing at idle 13 degrees ,rev to 3 grand and we have 31 degrees total witch in my books is great.Well it still pings,for the life of me why what do we do next?
Author: admin