Rhino is easier, no question there. You have the correct solution for the master I think, as the lettering will be the critical feature, one way would be to insert an etched mag plate into the side if you don't get the resolution you want or need. I have seen other repro attempts before, a problem can be the translucence of the gum rubber, your having a thicker side wall will help but, it may not be enough, might reference options before you pull the trigger. Also with that lettering I could see vac assist being needed to expell the bubbles trapped from the pour.

I would consider a hard core for the cavity, but may not need it.

I think filling the lettering with paint post molding is not a problem, I used some Liquitex acrylic on some later NOS Universals that did not have the paint fill, worked quite well, just wipe quickly and give it extra drying time.