First, I masked off the bumper opening with masking tape, and sprayed it with mold release. Then I wrapped some fiberglass down into the opening and let it set up a little. Then I covered the opening with some fiberglass.
Once that was set up, I skimmed it with some polyester body filler.
and then blocked the filler down.
Here it is all shaped and fitted
And here it is primered and painted semi gloss black
This is grill block works out well, but after monitoring the temp through my OBD2 connection and my ipad, I was able to see that the temp cycles up and down by about 10 degrees F about every two minutes, which is hard on the motor. I don't recommend a full grill block one one of these cars. I can still use this on one of my electric conversion Metros, but those don't need the airflow. Best bet on a gasoline powered Metro is a partial block.