Scaling to a set dimension

I must be missing a function! I am trying to design a stamp for concrete and for simplicity, it is a basic rectangle shape that I am trying to stamp. I have set dimensions that I want to chamfer or scale the bottom face to be able to remove it from the concrete. the back face is a rectangle that is 5/8"x4-1/2" and the front face needs to be 3/8"x4-1/4" and the stamp is 1/2" thick. Chamfering doesn’t allow me to meet those dimensions as far as I can tell. Scaling will make the drawing look correct, but the dimensions don’t work out correctly. Any help would be greatly appreciated.

I was expecting more replies. Can you share the design file? Your approach to scaling seems to be the proper method.

This is big dimension