thermostat water neck question

ugh!...But, I ordered the Mr. Gasket 4365 thermostat...it looks like the thermostat is too big for the water neck. I found another thread on this forum that suggests it is hard to find a water neck for the Edelbrock 7577 intake manifold, the magnum and later engines have a different water neck ?

I don't have the engine yet, I can check the water neck and if it fits get a smaller diameter thermostat...in the mean time, does anyone know a specific water neck for the Edelbrock 7577 intake and also the thermostat that fits it?