Hi Michael....welcome to the Club
Sounds an interesting project and story to tell of its tragic history.
The exhaust I can understand as open to corrosion with standing in water but the engine, if not turned over should be fine as wouldn't necessarily ingest water to the cylinders.
I would be tempted to remove as much of the anciliary items from the top of the engine and take the plugs out and fill with WD40, etc to turn over to clean the bores.
Obviously, the cambelt would need changing along with water pump, etc and I reckon it will clean up nicely internally. I believe the pistons have ceramic coating and wouldn't require replacing or even cleaning.
Let us know how you get on and photos of the condition as it would be great to see