You should not be getting pinging with what you are using.
1200 rpm is a little slow for full centrifugal advance.

I put the 75 electronic ignition system on my 122 wagon a week or so ago
and it is pinging but mostly because it is advanced probably 30°.
It also kicks back against the starter but it starts and runs well
other than the pinging and I am neck deep in other stuff so I will
re-time it later. Anyway I recommend the 75 electronic ignition. The
spark is a LOT hotter. I tried it out with a slimed plug and it burned
right through the slime and gave a brilliant white flash. I suspect that
with a much hotter spark mixture issues may be less critical.

BTW I agree with Rhys - the heavy oil and stronger spring are probably
helping you get over a basic lean condition.

BTW (2) I once had a broken "rich mixture device" disk that made that carb
run full rich all the time, fouled plugs, stinking exhaust and abysmal
gas mileage. It took 3 trips to the Panama dealer and a change of
shop management (from a Panamanian to a Brit) to find it. (That was when
I had first gotten the car, about 1972 or so.)
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma