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.
Actually other way around in most cases.
The muffler is the most restrictive part of the system. Larger diameter muffler tubes in and out generally help minimize that restriction. Laerger over all size of mufller generally helps make a quiter muffler. VEOTOM (sp?) has some good posts about mufflers.
The rest of the exhaust tubing should be sized for least disruption of flow and maintaining enough velocity at low rpms exhaust gasses are always moving away from the exhaust valves.

Really dont see how this will make a major difference in the timing.
If its a hot cam, with lots of overlap, it will need more initial than factory.
Also you've ditched the factory emissions setup, depending on the year, it could run better with more timing.
I dont have timing specs for the super 6 or anything that late so I cant be more specific.

For ballpark idea of what the timing should look like, non-emmissions, this is range for a '67 225 set to the factory 5* BTDC at 600 or so.
upload_2021-7-20_8-32-12.png