[SAJ]

Stage, my motor is the same as yours. Flow tuned jets, B carb, stipe cam, large inlets, 6 to 1 compression. Running 95 or 98 octane non-ethanol gas. With GAV open 1/4 turn W-6Y plugs were barely off white. I started to burn inlet valves at this colour. I now run another tiny bit more open on the GAV ( previously at half past on a clock face. Now right at 22 minutes past the hour). Plugs look grey in daylight. Camera makes them look mid to light tan for some reason. In photos Plug chop done after running about 1 mile at 55 MPH. Petrol consumption at this GAV setting 22.5 imperial mpg. at touring speed of 55mph. Goes up to about 23 mpg at 50 mph with GAV setting at leaner half past GAV setting
Car is 1930 roadster with full luggage and tools and 2 passengers, 3.78 diff, 26% Mitchell o/d and Excelsior Stahl radials at 38 psi front and rear.
With modern unleaded fuel, my exhaust pipe is black not grey or tan, and the old tan colour of plugs is now more grey than brown. See photos attached.
SAJ in NZ