Mercruiser 470 (1977) Thermostat Gasket

[mainexile]

Hello all. Been a while since my last post. Have a 1977 Mercruiser 470 with closed cooling that I'm replacing the thermostat on. Does the thermostat sit in the recess of the housing with only one gasket on top of it between the thermostat housing and the coolant reservoir? Some kits have both the oval gasket with two bolt holes and the square one with four holes.
Thanks in advance.
Steve

 

[mainexile]

Disregard, please. Replaced thermostat which helped some (square, four-hole is the only gasket required), but I'm thinking that the impeller needs replacement since the temp fluctuates at low RPMs but seems fine above 2000. Thanks for viewing.