Timing Question

are you sure it's pinging and not a leak around the exhaust manifold? i've had leaks before when i had my 340 dart, around the headers. under load they would be noticable but not at high rpms

if you are sure it's real ping, maybe swap out the orange box for a regular chrome

also make sure your plug wires are sound and the distributor cap does not have a crack.
a hairline crack in the cap will cause all kinds of weird stuff, you never know.