Why is this 360 pinging

NEED more info. It is very tricky to build a truck engine that performs well on pump gas. You really need to reign in the compression ratio if you are going to cam it properly-especially with stock exhaust manifolds-they are not very forgiving.

Jet up, try colder plugs, much better fuel (AV gas would be a great test) or dial back timing and live with it. Me? I would remove heads and add some cc's or get other heads with a larger chamber. Oh and carefully examine the piston tops while the heads are off-those KB's HATE pinging. J.Rob