To remove the grill, On the 451, you have to remove the front bump fender Assembly. You probably have to do the same thing, on your 453 model.
I owned this snap on trim remove tool for over 45 years now. You can buy Harbor freight plastic ones really cheap too.It looks like a push pin or plastic rivet as mentioned in post #3. Obtain a fork shaped tool and you should be able to pry the rivet out for removal.