Big difference in cam specs for dynamic compression?

No worries, that's what these forums are for :)

The lower dynamic compression ratio achieved with the 268 cam would help reduce the chance of pinging, but before you do that it's important to check that your ignition timing is setup properly as it is the single most important variable to eliminate pinging.

To begin with, try retarding the distributor a fraction or two at idle. If this makes the car run rough (even slightly) you've gone to far

Common practice is to find a shop that will change the ignition curve of your distributor to suit your camshaft. In my experience this usually costs about $100 and makes a world of difference to your engine's overall performance.

You can also experiment with different head gaskets to increase the combustion chamber volume. summit racing has a pretty large selection.