Framelines substitute for Super Ikonta A 531

[robert_ante]

I acquired a Super Ikonta A 531. Late model with coated Tessar lens. Camera is in immaculate condition.

, ....except....Except for the common condition afflicting these cameras        viewfinder frame lines have.

completely vanished. I assume that replacement finders for 6x4.5 cameras are not available. 

I was considering attaching a mask of some sort to the front lens of viewfinder for 6x4.5 negative. I can do without

viewing what is outside the frame. If such a mask were possible, what would be its dimensions?

Which is better, to mount on inner or outer surface of VF's front lens?

 A view slightly smaller than would appear on negative. would be preferred to one showing more

There is an old thread on this topic, but suggestions were to use white ink to draw lines, but no

mention o the dimensions of rectangle or placement with regard to frame holding front lens. I believe a mask

would be simpler, but I am open to any suggestions.