That is a medium mild cam. my guess first off would be vacuum advance hooked up to manifold vacuum.
First off vacuum advance should never be hooked up till all your other tuning is done. my second guess is stock distributor springs not allowing what little mechanical advance to come on till 3500 or so.
so say this is the first too problems say you have 35 total but that total includes 20 deg of manifold vacuum and the 20 deg of mechanical is not all in till 3500. So that puts you pre start up initial at -5 deg. At WOT there is no vacuum so when you floor it at 2000 rpm the vacuum advance is gone and if all you have is a slow curve mechanical left you are probably at 5 deg of advance or so and that is so slow. then as your rpms increase to past 4000 the motor needs advance but you may be at 15 deg of total advance so no go either.
I could be wrong but I seen this lots!!

I would unhook and plug vacuum. set total to 38 deg with lighter advance springs having it all in by 2000 to 2200. when ypu have it all tuned in right see how it works. then and only then vacuum goes to the ported vacuum and any pinging is tuned out of the vacuum pot with a 3/32 allen wrench (in through vacuum pot) going counter clockwise till you have no ping under all types of driving!