Thank you, Oristo and DJ7BA ---
I discovered the small metal shim or bezel at the bottom of the viewfinder shipping box this morning before I read your posting (did not realize that the shim was included, or that the viewfinder used magnetic mounting).
The shim or bezel has four thin adhesive areas used to attach the shim to the camera body. I slightly trimmed the shim at one corner (it had slightly enlarged outline, perhaps to help camera owner to position the shim, but in this case the enlarged outline interferes with one of the four nanovna screws), then pressed the shim onto the front of the nanovna.
The shim does not adhere very well to the front of the nanovna; perhaps because of the material or paint used on the front layer of the nanovna package, or I impaired the shim flatness after trimming the corner, so after I attached then removed the viewfinder (the magnetic attraction between the viewfinder and the shim is quite strong and magnetic attachment would be a good solution to problem #3), the shim separated from the nanovna and remained attached to the viewfinder magnets.
The presence of the shim (it is ~1mm thickness, adding to the distance between the LCD display and the viewfinder lens) did not seem to change the image focus enough to notice - it was still slightly out of focus (with chromatic aberation), but perfectly usable. I would be happy to use it.
Considering the intended fit of the viewfinder and the very good fit otherwise to the nanovna, perhaps the nanovna 2.8" display was originally used in digital camera manufacture...
I think a more useful solution would be a replacement nanovna 2.8" front panel made from thin steel rather than FR4, but with same opening and same mounting holes. This would allow the viewfinder to directly attach to the nanovna front using the in-built magnets. It is probably required to use commercial manufacturing to make a steel front panel, so I do not think I will be able to proceed further, but I will investigate improved attachment of the viewfinder for my nanovna.
DJ7BA - I did find other listings of this type of item on ebay, some lower price maybe USD 6 with (slow) shipping. There seems to be some variations depending on camera type. My device was labeled on box as type "V1", type AY014, for Canon 5DII/7D/500D and Nikon D700/D800". I have no such cameras, so I did not consider the possible differences.
Thank you again,
Dave
