Pull up the ASME tables on torque. The plate is nothing but a flat water jacket cover. Good idea replacing the stat and PO. I clean up the mating surfaces and use a sealer on the gaskets since some corrosion is commonplace, unlike new engines that get put together dry. I use a thin film of Blue RTV but some people squeal about that saying it floats around in the cooling system and clogs things up. I don't use the whole tube on a job and never had a problem....not making a gasket, just filling holes caused by corrosion with a thin film.
Other thing on removing your screws, squirt with a good penetrating oil and use impact, don't get on a bolt and twist till it comes loose or "breaks"...on a 16 year old engine, fresh or salt, corrosion can cause bolts to seize and they aren't very hard to twist off even though they are SS. One of the guys on here says he grinds the heads off, removes the plate, soaks the threads and then using a vise-grip pliers unscrews them.
Once you get them out, dress the bolt threads with your grinder's wire wheel. Then take a 5/16 fine thread (as I recall) tap and chase the tapped holes in the block. When installing, coat the threads with blue thread sealer and torque per wet thread specs if you choose. I never torqued mine as I just worked on my own equipmen, had nobody to answer to and never had a call back!! No big deal, if you have 12 psig of water pressure against that plate you are at the limit as to what you can expect for water pressure. I do secure in 3 steps starting in the center and making an expanding X. If one spot leaks, just tighten the adjacent bolt till it stops or torque it.
Everybody has their way. I gave you mine.
