They are different, the 103 uses a non-gasket taper seat plug, whereas the 104 uses a regular gasketed type plug. If you use a F8DC4 in a 103 it will work but the plug won't extend fully leaving a couple of threads of the spark plug hole exposed to the hot combustion gases and will quickly carbon up. You will find that the gasket becomes very distorted fm trying to seal against a tapered seat. When you eventually try to install the correct plug you'll have problems seating it fully because the last few threads will be fouled w/ carbon.
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