G'day Sprint. It also depends on the octane rating of the fuel you use. The higher the octane the slower the burn so 98 would need more advance than 91.
I use the old "advance till it pings then back it off a couple degrees" method. I run 35 degrees in the cafe but use 105 octane fuel and 9.5:1 comp, if I put 95 or 98 in her she pings badly. Any more advance and she pings her head off with the 105.
I think Orabanda worked out 32 degrees is best for his iron heads.
Cheers