G_G,

My NOS Monza came on a Rally strap, probably Corfam, since I have seen the exact same strap signed Corfam on the back. Definitely not rubber or Tropic Sport. The buckle is black and unsigned.

I think your Monza would would look a whole lot better on a Hirsch Rally strap than it would look on a Rodania one.
I've had a few Rodania straps and I find 'em rather wimpy looking.

This is what a Carrera looks like on a Hirsch Rally:

You could always take a black Sharpie and turn the white stitching into black.

Good luck!

Darwin