make sure that the vacuum advance hose is attached to the fitting at the center body of the carb. this will give you ported vacuum and cause the advance to only be there when the rpm's are above idle, if it is hooked up to manifold vacuum, it will have advance all of the time and it will affect your performance. the way to tell is when it is idleing, take the hose off at the distributor and put your finger on the end of it, if you can feel it sucking, it's hooked up wrong.
when you set the timing, disconect and plug the vacuum hose at the distributor, that way you set it with only initial advance. and like I suggested before, set the timing at 10 degrees, it will run better still and shouldn't cause it to ping.

so you know, the 71 1200 did not have EGR, if you are refering to that pipe at the left rear of the block that is about an inch round and a hose going to the intake manifold, it is the PCV system.
the PCV system and a primitive vapor recovery system are all the emission controlls that they used on 71 to 73 USA models.