water pump & spark plugs

Two questions here:
First: The plugs that were in motor of my 1962 40HP were J4J. The plugs have been in motor for the past 30 years sitting. When I went to replace the guy did a cross over & gave me J6C. Now I put them in & engine fired up nice BUT should I use them?

Second Question: I asked a while ago about how I should run motor & all said it should be in barrel NOT the hose hook ups used now a days on newer models. Now when motor is running in water barrel just spits out of exhaust hole rather than stream. Is this normal? One video I watch said it was but was a newer motor. Haven't run motor for any long time due to this. Maybe need new thermostat? Maybe need everything? LOL

Like I said this boat has sat for 30 years since 1990 but all seems to be working so far.

On the boat at full throttle water would pour out of that hole.------When you slow down at the dock water ( and water vapor ) would pour out of that hole.-----Some would say it is steam.-------Then when motor cools it starts to spit again.

Thank you. So the best place to start is with thermostat in case stuck with age & then move on to impeller.