In dash cluster aftermarket tach replacement-69 Cuda rallye cluster

Not sure you can actually do that. The mounting holes for the tach are offset so i can only be installed oriented 1 way, ditto for the blankoff plate. If you turn it around all 3 of the screw holes wont line up.
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.