Help on 408 build

Only a guestimate but it sounds like compression is in the high 11s assuming zero deck height and with that smallish cam and that total timing im not surprised it is pinging.
Depends on what you want to spend on it now but most stock 360 heads i have cc'd have been around 72cc and if you put another pair of heads on with a slightly bigger cam you might get away with it without pulling the short block apart as compression would be in the mid to high 10s. This option would leave scope for later if you decide you want to step things up with a bigger cam and alloy heads,once you get used to it you may want more,it happens!
That cam is going to peak very early being in a 408, i have a 248 at 50 solid flat tappet in mine and it is still very streetable.