Performance Distributor in Stock Engine

With a '67 273, I stay with a stock distributor curve and just experiment with some more initial.
By that I mean set the initial timing a little higher and see if its a little more responsive, with no pinging at part or full throttle acceleration.
IIRC, the initial for Plymouth was 10* at 600 rpm or 650.
Try 12* or 14* (you'll have to reduce the idle speed screw a little to get the rpm back down to 600 or 650)
Depending on the engine and fuel available to you, the engine will like at least 12*, and prob 14*.