This will stop the leak.
Thermostat Housing Gasket
Install EXACTLY per the manufacturers directions
My intake looks exactly like like yours. I bought an aftermarket repo t stat housing
And have not had a drop of coolant in 4 to 5 years 16 lb cap.
ALSO...
be sure the screw holes in the block are clean. Screw the bolts in and they should be able to screw in and bottom on the head before the bottom of the hole.
