Looking at installing water pressure gauge on 502. Where is the correct (best) place on engine to install sending unit?

Mine our on the intake manifold so they don't get plugged with sand or dirt. Do a search you will find several posts on the subject.

I have mine in the intake manifold as well. Using the block drains will clog up with sand.

What they said.

Thanks, that's what i was thinking.

what is the ideal water pressure for lightly modified 502 with bravo?

Search Function returned 4 pages for your reading pleasure.

Mine was factory located on the oil cooler h2o drain (Fountain).

I like that place.

Merc suggested to place their water pressure regulator (available thru any Merc dealer if it's needed) after oil cooler and before engine inlet.