I seem to remember these were advertised once, but can't remember where.

• Cut the window spaces in the cab front – I would clamp to the drill table and use a tank cutter very slowly.
• Remove the centre drill from the tank cutter and use it to cut two disks of plastic (you may need to change the setting depending upon the shape of the cutter).
• Chuck a large piece of metal in the lathe and hollow out the end about half an inch or so to leave a thick walled tube large enough in diameter to allow for a ring of 8 or 10 or 12ba bolts to hold it to the cab front outside the round window, but with a bore that is a bit smaller to hold the plastic in place.
• Drill holes for bolts in the frame – I would use a tool post drill, but in the past I have made a guide that I have held in the tool post and used a hand held drill.
• Part off two slices and you have your frames. Drill holes in the cab front and bolt frames in place with plastic in between.
• I would probably face out the metal enough for 2 and a bit frames at a time before drilling deeper and facing/boring deeper for the second pair taking the size from the 'bit' still there after parting the first set off.

Yes – trapping the glass between screwed-together bezels is a typical practice.

Putting the screws through the spectacle-plate too, helps keep the bezel width down. The outer ring could be of T-ring form, its very thin up-stand slightly less high than the plate thickness, to locate it concentrically and to hold the glass. Spot-drill the spectacle-plate from one of the drilled bezels, being careful not to widen the holes in the bezel.

I wouldn't add the complexity of opening windows, unless perhaps you are fitting a full cab. As I recall the Tich "cab" as designed is no more than a spectacle-plate plus a couple of low side-sheets.