'84 Black Max 200 water exit question.

[donzi gt230]

I have a severe over pressure situation on one motor, it was like that when I bought the boat and the PO had no idea about it. He just said it takes longer than the other motor to warm up. I'm pretty sure the problem is a wrong gasket or something at the base of the powerhead, but would like to see a diagram, or better yet a photo or two to know what the passages are like between the motor and upper. It seems that the poppet has a separate exit just based on the fact that it won't warm up until I start putting a load on it; indicating to me that the poppet is letting water flow at idle.(?) I've found only one photo of the exhaust plate but I'm not sure if it's the same thing that's on my motor. In the photo there were two large squarish ports (I assume where exhaust flows) and two narrow rectangular ports (I assume where water flows). Is this correct? Looking at the amount of rust on the powerhead studs has me scared to try to remove it, but I just can't bring myself to run it this way. I've had the boat about a year and only the maiden voyage to speak of. Also, I've read that getting the correct base gasket can be a challenge. If I have to do it, will it be obvious looking at the new gasket that it's the right one? Is it just a matter of it not blocking any ports? Is there even a reason to not use RTV or something else instead of a gasket?
THANKS!