Just add 3 nuts ans bolts on the Mould, and 2 nuts and bolts on the Stamp, all of those, stacked aligned, for a smooth surfasce.
Engrave your Adress, Logo, whatever, on the Stamp's face, remember, reversed.
Spray a layer of the proper anti-adhesive, so the Material won't glue itself to the Mould.
Pour the Oogoo, Sugru, whatever material you can pour or plug into the Cavity;
As the Acrylic is transparent, you can see if the casting is ok,
Plug the Stamp into the Mould, wait for it to cure, that's it!