The right way would be to change out the housing but the restrictor should work. The Merc water pump is capable of moving a ton of water AND the flow of water is already restricted in the factory system anyway - shouldn't be a problem to experiment.

Actually, the right way would be put a circulating pump and bypass-style thermostat housing, but that's not the subject here (at least right now).

Now Ive read that experimenting with a restrictor plate could help get some heat into the engine (a good thing) but may create too much pressure in the block....and, as said above, will also not get enough water to the exhaust.

If you look at the tubing used to move water around versus what comes out of the pump, there shouldn't be an issue. Water pressure in the block shouldn't be an issue either - nothing is closed off and water is going to free flow. You're just slowing it down some to let some heat transfer occur. So long as the risers do not get too hot you'll be fine. You want the water temp at the thru-hulls to be about 140.

Would drilling a couple of 1/8 holes in the thermostat work?

Thanks for all the input. So here are my options/considerations. The more I read, the more conflicted I get.

1) Add a bypass to my crossover system and put a 140 thermostat in there with 2-3 small holes drilled into it. In this scenario, is there any concern with the cold bypass water that sits on the top side of the closed thermostat causing erratic temp issues? Basically counteracting the hot water on the bottom side of the thermostat that is telling it to open? A kit like this is what Im thinking:
https://www.hardin-marine.com/p-1335...th-bypass.aspx

2) Play around with the restrictor plates to try to get more heat transfer. If I dont need to worry about too much block pressure or not enough water flow to the exhaust, this sounds like the way for me to go.

Not trying to PooP on what you have but it is plumed all wrong. I am not even going to touch on the circulating pump thats a another issue. Most 454/502 motors have a thermostat housing with 4 outputs. 1 to each manifold and 1 to each riser. you have plugs in your risers. . This is he way it should look and have a 160 thermostat in it.

https://www.ebay.com/itm/40425773080...BoCvbAQAvD_BwE

If you look real close, it looks like his risers have wet joint.

they have a wet joint that’s plugged off with a blue plug

If your risers are staying cool, you can make what you have work - you cannot run a thermostat unless you have a bypass going from the crossover to the thermostat. The restrictors will work without having to change what you have.

If you want to run a thermostat,... your crossover has a bypass fitting and you have a plug on top of the t-stat housing. Put fittings in those two and connect them with a 3/4 to 1-inch hose. Water will flow through the path of least resistance. Once the thermostat opens, water will flow more from the engine side vs the bypass. Monitoring water pressure is a good idea (running a crossover or not).

Helpful information:

https://www.offshoreonly.com/forums/...er-bypass.html

https://www.cpperformance.com/p-1335...th-bypass.aspx

TZ