1997 Mercury Cougar rapid knocking sound

It started from getting the car stranded in flooding water. Pulled it out changed the oil right there beside the creek. But when started the car it was knocking seemed like 2 differant sounds. One went away the other sounded like maybe flex plate so changed it. But still same noise. Ive changed oil 3 times haven't driven car since. Guessing it may be a lifter? Not sure because it don't seem to be missing. And the knocking seems to me to fast for a main bearing. Just wondering if you had an idea before I start taking it apart. And the car wasn't totally submerged. But the oil was milky.
Ps was wondering if a 32 valve motor from like a markvIII would be an easy swap like work wiring harness and all