I'm using Champion 7405s in both my 401 and 304. I went round and round with plugs for a while, trying to treat other problems with plugs, but stem seals and intake leaks will foul any plug. I started with the Champion copper truck plugs and they fouled on holes 5&7 every couple hundred miles so I switched to Autolite platinums (like $7 a piece). After swapping the intake, carb and valve stem seals I switched back to Champion, but this time ran the platinums (7405s) and I'm happy with them.
From my research, using a high energy multi spark ignition with platinum plugs makes the temp range far less critical. Most platinum plugs are a "colder" temp rating because the platinum itself resists fouling. It's a noble metal so it doesn't oxidize allowing other materials to bond with it like copper or nickel. From my understanding, this is why most platinum plug manufacturers only make one or two plugs for each size instead of a range to pick from. If they make two, one will typically be much cooler and listed as a "racing" plug.
For those that want a quick primer on Spark Plug Temperature, it has to do with how much of heat the ceramic insulation carries out of the engine (to the plug wire boot end). If it takes away too much heat, the plug cools too much between sparks which allows the red hot electrodes to collect carbon and oxygen (fouling). If it doesn't take away enough heat, the electrodes stay so hot during the intake stroke that it can ignite the fuel/air before the spark plug fires. This is far more critical with low energy ignitions.
EDIT>>> In case you care, the reason I went with the Champions is that at the time, they were the only platinum plugs for our trucks not made in China, (they were made in Mexico). Don't know if they still are.
Double EDIT>>> Just went and checked and I still have 3405s in the 304, 7405s in the 401. The 3405s are the cheaper champion platinum. Seem to be adequate if I forgot that I hadn't changed them since 2011.