I agree with the OP, stop chasing the plugs. Both numbers are correct for that engine. The timing of your plug change could be a coincidence.
Watch water pressure when the alarm hits - low PSI possibly? Check the impellers or consider the complete water pump rebuild kits and new thermostats...
As someone who owns and operates a professional marine fuel injector service shop, the issues with *new* knock off injectors is 100% real. I know it's tempting to buy knock offs at a discount. Even if the fuel injectors spray well and are flow matched to your existing set, you just don't know...
