Drill two small holes through the skull plate at the thickest part. Hold the antlers on the plaque to check their position. They look good about a third of the way from the top. Drill corresponding holes in the plaque.
If you don’t want the outline of the skull to show, you can tape foam around the skull plate and between the antlers to give it some shape. Alternatively you can use clay to build a moulded shape for the skull plate.
Cut a piece of leather [or deer skin or velvet etc] large enough to cover the skull plate plus half an inch to go over the edges. Measure the distance between the antler burrs and cut those holes out of the leather where the antlers will be.
Stretch the leather over the skull plate with the edges rolled under so it is free of lumps and indentations. Fasten securely with tacks on the underside.
Place the skull plate on the plaque so the pre-drilled holes in the plaque match up with the ones in the skull plate.
Secure the skull plate using two long drywall screws.
Some people attach a small photo below the skull plate or include details of the date and place of the hunt.