Does anyone have experience with V/P I/O Marine engines?

I have a newly rebuilt '84 Volvo Penta I/O marine 350 in my 84
Bayliner. About 10 hrs on it since the rebuild. I think / hope that it
was winterized correctly- oil change, ran anti-freeze through the
system, etc. . When commissioning the boat a week ago, we checked the
oil before starting it. It looked OK. After running the engine for
about 3 minutes, we checked the oil again and it looked like a vanilla
milk shake (water in oil!). I pumped it out, fogged it, pumped that
out, put in 5 qts of new oil, put the ears on, ran it again.... Same
problem. No freeze plugs popped.

Do you think the block is cracked? If not, can anyone tell me what
potential areas I should look at to find the contamination point
(water leak to block / oil)?

I only spent $3K for the boat and now have about $9K into it. It's
getting frustrating.