1975 Mercury 500 thunderbolt 50hp 4cyl - what is spark plug #?

[tunerauto]

Doing the maintenance on my newly acquired boat and I want to replace the plugs. Im getting the Selco manual for it but till then I will have to ask alot of questions. I also dont have a o/b store readily available so I will have to order alot of my stuff.
Question is , what Champion or NGK spark plug number do I get for this motor?

 

[Aqualift]

Re: 1975 Mercury 500 thunderbolt 50hp 4cyl - what is spark plug #?

AC-V40FFM or Champion L76V, OR NGK BUHW

 

[tunerauto]

Re: 1975 Mercury 500 thunderbolt 50hp 4cyl - what is spark plug #?

Thank you , Gap?

 

[Moody Blue]

Re: 1975 Mercury 500 thunderbolt 50hp 4cyl - what is spark plug #?

These are surface gap plugs. No bent electrode of the end of the plug, hence no gap to set. They are what they are.