Rather you than me to be honest.
V8's leak. So to just put it into water i would rather not do.
Unless you've sealed your inlet manifold, valley gasket, dipstick, bellhousing cover, rewelded the airbox as they leak, plenum, fuel tank breathers etc etc etc i wouldn't do it !
Alternator ? Starter motor ?
I've 'swum' before.....only to find a small leak on my fuel tank breather. I run multiple pumps each with filters so got away with it but it took me ages to get all the silt out the tank !
G