At this point I'm going to say you need to look into the PV as has been suggested and also look at the TDC mark.

Try backing down the timing and see if it goes away. If it does and runs good(not a slug), chances are the TDC mark is off.

It has been awhile since this got going, so i don't remember what the plugs look like. Are they bright white and clean?

I've pulled the timing back to 19* initial and 33* total. It still pings. It wasn't a slug at that timing though. My initial timing, the vacuum at initial, etc. all suggest to me the TDC mark is fine.

I haven't checked a plug in it in a while but they are so dirty from all of that I've done I'd really have to throw in a new set and check.

I think I'm going to take it to a local guy that does a lot of work on these BB Mopars and let him have a look. His opinion over the phone was that with pistons .100 in the hole it is always going to ping.