I have this fan (1953) still running. The grill attaches with two fairly long machine screwswith large heads on them (somewhat decorative) These heads hold the grill up and in place. Assuming your grill is rectangel, the holes through which these enter are exactly in the middle long axis of the the rectangular grill;...throught the slots themselves there is NO hole for the screws visible, but you can see the receptacle holes in the motor fan housing itself, each in the midline and lining up with the u end of the middle slot. My grill has 9 identical slots, so slot 5, in the middle. The heads on the screws are about 3/4 inch in diameter with ribbed edges to make them easier tot turn. screws are 3-4 inches long, and may be variable depending on your installation. The screw heads look to be solid bright aluminum to me. That might help you identify them in a wayward parts jar. Hope this helps. If you need, I can supply a photo to help.
Again the screws align with the outer most ends of the middle vent slot in the grill...just look up into the unit. Steve
(sgriswold@me.com)