In dash cluster aftermarket tach replacement-69 Cuda rallye cluster

Yeah the blank filler is more plastic cup shape. Closest thing to a flat plate would be the back plate taken from a vacuum/performance gauge.
My vacuum gauge doesn`t work ,I have since gone to an aftermarket gauge in a diff. location. Any suggestions on what to do with the center gauge space now ? The vacuum gauge is still in it, I don't really want to pull the dash !!