I just replaced Bosch platinum plugs on a 429CJ and the hot hard starting problem went away. Starts better and runs as good or better. The Bosch plugs were the type with the electrode buried in the insulator.
Never had this kind of a problem with plugs in many decades of working on classic Ford cars. The auto parts stores are selling them as a direct replacement on the older Fords, (as always its better to do researce on your own before buying after market parts). The probem started the minute the plugs went in.

There are a number of web sites with some of the same type of comments about the Bosch plugs. My two cents stay away from them on the old Fords.

 

Bosch relays work good as relays. Bosch O2 sensors work good as O2 sensors. Bosch spark plugs work good as fishing weights and should NEVER be mistakenly installed in an engine unless it too is to be used as a boat anchor.

 

nothing wrong with BOSCH. brilliant spark plugs in the wrong engine. what you want is autolite copper cores. they are what should go in

 

The Autolite mentioned is what went back into the motor. Just as a side note a couple of the issues with the Bosch, (not mine) seemed to be related to loose spark plugs. If the plugs get loose they over heat. At any rate back to the Autolites for me.

 

My 97 5.0 DD got Motorcraft double-platinum at 80,000 miles. Noticeably smoother, and about 1mpg better.

 

I have the 4 electrode iridium/platinums and can honestly say there is no difference between these and the cheap copper ones. They sure look nice tho. I still have them in car but would never buy them again. The electrodes get really hot and cause pre-detonation in my 2v. Premium solved this issue. I have a 93 octane tune in too tho

 

Autolite 3924, adjust heat range as needed.

 

and If using an MSD ignition system MSD says "DO NOT" use Platinum plugs!