7.4 MPI 454 Block swap

Hello everybody

excuse my spelling upfront i moved from Germany and English is my third language and i am not really familiar with the big blocks and what not
i used to be a mechanic though so i bought a 2001 Bayliner with a 7.4 MPI Engine the engine coolant was mixed up with fresh water trough a damaged heat exchange unit and of curse frozen over the winter. what i tried first
i reinstalled the water plugs on the block had to weld one exhaust and the engine was actually running ok but as i checked the oil level i had water in oil so i left it for a couple weeks now i have water in the oil compartment all the way up
my question now what would the pros recommend me in those cases in general

from my searching i guess its a 454 big Block
-i assume i have to replace the block ? or can the water went in trough the heads ?
-can i use a big block out of a car ? which cars/ Trucks ?
-should i replace it with the same block and swap the rest or is there a better alternative if i go trough all that trouble ?

Thanks

Arnold

Your motor may have a cracked block. Remove the intake manifold and take a look for they usually crack just below it.

Good luck.

Jeff

PS: Your English is better than some of the clowns in this country!

A remanufactured engine is not expensive if you do the work to install. A 454 is about $3500-4000. I would replace the engine and put on new exhaust manifolds and elbows just to be sure that it will be completely safe. Only use engine designed for marine use. Automotive engines are different.
It's going to cost you less to just replace. Rebuilding what you have can be far more money with machining, parts and your time.
A marine surveyor would have found this problem and saved you the time and money that you are about to spend on this boat. Next time maybe pay the couple hundred for a survey.

You should look at these guys https://www.michiganmotorz.com/remanufactured-marine-engines-c-31_51.html

if you can find a way to lift the engine or go to a shop that can lift it out it’s not too bad of a job to change the complete Engine

Better to shop a good used 496 MAG and replace the 7.4 with a good engine.

Thank you so far

about a marine 454 big block I saw there are different generations of that block
can i use any of those blocks and just swap everything over or does it need to be
lets say Gen VI which i believe i have ???