Can you take pictures of the intake and carb? What distributer did you use? can you see a number on the distributer? 273's were relatively high compression since they were never a smog engine. Disconnect the vacuum advance, and time it to 35 degrees total advance, that should work, then check where the initial timing is. Drive to check if it pings. If not, reconnect the vacuum advance and check for pinging. If it pings you are getting too much vacuum advance at part throttle. Luckily Mopar vacuum advance cannisters are adjustable. Use a allen key and "Turning it clockwise ('tighten') will REDUCE spring tension so advance is very responsive to even low vacuum levels. CCW ('loosen') compresses the spring, meaning you need high vacuum conditions to get full advance." from DodgeCharger.com Forum.