Spark plug conversion chart vintage outboard

[Cballer]

Curious if anyone has a spark plug conversion chart they can share ?
What I’m looking for is champion J6J and Autolite A3X are recommended in vintage outboards of the 50’s. I have a AC M45 in a unit right now not sure if it’s correct.
Trying to sort out for a friend he has 51 Evinrude 7 1/2 hp fleetwin.
Working on a few different from 50’s so chart could help a lot. Thank you

 

[racerone]

Rule was small OMC motors from 50 / 60's with thermostat used J4J ( J4C ) and without thermostat used J6J ( J6C )

 

[Cballer]

Ok thank you, the motor has in it now a AC M45 we are trying to determine if this is a correct cross over plug or find conversion chart.
Appreciate that knowledge I did not know that. My understanding the number on that plug you speak of is how hot or cold it burns so that’s logical information thx!!

 

[racerone]

No ---that number refers to how the plug gets rid of heat.-----

 

[Cballer]

Ok thank you