The color of the plug is good but according to my experience is too hot to run even on a street car.
I'm very surprised that you can use it.
Using the Ford Motorcraft chart as a reference, the coldest plug to run would be a 22. That plug will very quickly foul at idle. It would be useful for a track only plug and takes about 3500 rpm to clean them up.
The 32 is a good compromise and I have run them on the street with no problems and on the track to over 7,000 rpm.
The 42 is useful with something like aluminum heads and Webers IF you are having problems fouling the 32's.
I am using an NGK BP6ES. If you look at where the BP6ES NGK matches up to other plugs heat wise, it's hotter then the 32 but cooler then the 42 so it makes sense to me why it runs clean for me.
I suppose it is possible to come up with various alternatives but I stop when I find something that works.
An Autolite 3923 is in the 347 in my GT350. It's got AFR aluminum heads and two 600 cfm Holleys on a C60E Ford Trans Am intake. The plugs look about right so far. Cleaner then the Weber plugs but the same heat range.
That Autolite plug, 3923, will also work in a Cleveland with aluminum heads. It just uses a 5/8" spark plug socket rather then the 13/16" on the NGK.
IF you are using a high energy ignition system, there should be no need to increase the basic temperature of the spark plug.
Long ago I had tried to make MSD ignitions work and for the most part, they don't do what they are supposed to do and certainly are very unreliable.
The Ford solid state igition is a good system but it won't fire a fouled spark plug. With tuning Webers that often is a problem since it is so easy to go to over rich in just one jet change.
The best solution that I have found to use the the Pantera-electronics system since it will fire and then clean up fouled spark plugs. This helps tremendously with tuning a Weber carburetor system.
These are just my experiences, not necessarily a formula for anyone else to run. Obviously others have had different results.