I noticed that my port engine was running more water pressure than my starboard engine. The starboard engine runs about 35 psi but the port engine pegs the gauge 45+. The oil pressure is slightly higher on the port engine as well. The starboard runs about 40psi and the port 50psi. Is this anything I need to worry about?

You need a pop off valve for both engines. 45psi is way too high and 35psi is pushing the limit.

Closed cooling likes more pressure but 45+ is pushing it.

I have pop-off valves and I know they do relieve some pressure. Would a stuck closed thermostat cause this. I am going to pull mine tommorow and take a look. Anything else, anywhere else I should check?

Fresh or salt water boat? Clogged risers will cause increase in water pressure too.

Fresh water

I doubt a stuck tstat would cause it, unless it was overheating also.
You can take the pop off valves apart and cut the springs down to reduce the pressure more.

Are you running cross overs or circulation pumps?? drill 3 3/16 holes in the thermostat, that will relieve some pressure.

Where are they exactly located on the 502 MPIs? I know I have them just not sure of the exact location.

They are not a stock item,,their would be through hull fittings where the excess water will dump through..

If thease are stock engines you will need to install a set of water relief valves and the plumbling..