Dolphin gauge insert

[expedition]

Hi there I got a dolphin gauge set with the aluminium insert for my 64 gmc truck ,not sure how to fit the insert on my original cluster plastic frame .I already cut out the old gauges contour leaving the lip on ,does insert plate mount in front of plastic frame or behind it ? If I install the thick plate plate in front of frame there not much room for the screws to fit in to the dash .Anybody as an idea on this ?Thanks