Distributor recurve

The reason I'm fudging with the distributor is I already have "a lot of detonation and lousy fuel economy" (15 mpg in town). My goal with the distributor is to reduce the mechanical advance to eliminate the ping.

I have stock 2" exhaust all the way back. I think the Super Six cars came with a 2.25" pipe. I asked the muffler shop to give me a 2.25" pipe with a 2" muffler, but the guy convinced me it wouldn't make a difference. I think he was wrong and I am considering telling him to do it anyway. This is what I am looking at:
and maybe this:
and maybe even this:
I don't want excess noise, but I do want the engine to run well.
You do not want to reduce the pipe size at the muffler to 2 inch, that would restrict flow - bad dawg!
Run the whole system in 2 1/2 inch and be done with it.