F**K YOU TAIWANESE/CHINESE MADE JUNK

I don't think I'd grind on the thermostat- those halves are crimped together around the outer edge and the last thing you'd want is a bunch of little parts swimming around in your radiator and water pump. Bite the bullet and get a different t-stat housing.
This thermostat is not that type, taking a smidge off the edge will be fine. Also I may cut the recess a little bit bigger which is not a hard job to do, but it so sure does suck when I have to fix new parts.
Will the old one work? If so, I'd just use that one.
Maybe with lots of RTV lol. It's really bad, that why I'm replacing it.
What intake are you runnng? Most aftermarket intakes have the recess the thermostat fits into.
Edelbrock 2176 Performer, there is no recess.
I'm not seeing the size difference in the original photos since the thermostat flange is obscuring the recess?
It's just about too small.
Where did you purchase this from?
Summit and whoever is the lowest bidder for Summit.