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Its 2005 - crab type. GM/NAPA does not have brass studs so statying away from them,a "350 MAG MPI" could have had at least three different styles of distributors....
If its the newer HVS type (a crab cap), I'd go with a Mercruiser OEM cap or a GM part.
If its the EST type, you may get away with either.
If its the older T-bolt type, I'd go with a Mercruiser OEM cap...if you can get aftermarket with brass terminals, they can be ok...
I would think vented is not a good idea on enclosed gas engine compartment?Interesting Summit Racing has brass caps with a vent to reduce moisture. Are Mercury/Sierra vented? Is vented a good idea on a boat in salt water environment? https://www.summitracing.com/parts/sum-g5225
Ayuh,..... Either a metal screen, or a brass elbow,.....If there is a vent hole, it should have the flame suppression screen in it...I believe Mercruiser had a service bulletin on the topic years back...