water heater removal? how to close engine cooling loop?

We’re thinking it’s time to remove/repair/replace the water heater (6 gal) on Hopalong (FreedomExpress 39 - 1984.)
Any advice on closing engine water cooling loop if we do need to remove the heater tank? ( we have a Perkins 4-108.)
We’ll be returning to Mazatlan next week. While we hope the heater itself can be saved, age of boat suggests otherwise. The heating element itself has been out for some time but warm environment means it has not been missed.
So any help on this will be appreciated. Also, if you know specs for element replacement, we’d like that too. Thanks. Sally and David

There’s no issue removing the tank. Simply loop the engine water loop back to itself either at the water heater or at the engine. I’d go with the former in case you ever want to replace it.

– Geoff