My 72 started running rough today, I have a Pertronix unit in the dist. and just had the Eldebrock rebuilt a couple months ago and was running good, but today I barely got it back home, motors a stock 283, nothing fancy, after it cools was going to take a look at plugs and I think the hamonic balancer slipped or I got the dist. in wrong as timing was at 40 degrees, but ran fine till today, any thoughts?