You have to trim the top edge and the sides to let the rad into the panel so that the rad sits tight to the upright of the front panel.
Here's a pic of one that's done

5429870-garage.jpg (310 downloads)
69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200#
best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft
best 60ft 1.36