i have a 455 olds that that is going in my boat it had a 455 in it that was blowed up so i found a replacment i am getting hardin marine exhaust logs/snails for it the old berkely logs were cracked way bad my question is do i keep the engine mounted water pump or just use a pump plate? and how do my lines run from the jet pump i read a few things saying i would need to install a gate valve to regulate water pressure is that true thanks

Also do I run a thermostat or not?

that helped out alot thank you so much  now what about regulating the pressure of water going to the engine do i need to do anything for that

that works for me thank you very much for your info i am new to jet boats

It's still a good idea to have a gate valve at the jet as a safety feature.  If you have a hose failure or blow out a freeze plug you can stop the water flow by shutting the gate valve.

You're 100% right CC, I spaced that out.