You don't need plexiglass or glass. You can operate a Keymatic with the door open.
On a Keymatic the door boot is VERY floppy and flexible, it needs to be. The drum moves around a lot more than newer machines. The drum is suspended on a cable and two very soft springs, as the drum fills with water it drops till it is sitting on a lip at the front of the frame, then the drum keeps lowering at the back so it tilts back as it fills. So when it is full the water level is higher than the top of the pulsator at the back (that is, more than half way up) but below the rubber seal at the front. The combination of the severe backward tilt of the tub and the deep door boot means only a few drops of water splash out when you do a load with the door open. (You have to bypass the door switch and disable the drum brake - Unlike most front loaders, the Keymatic has a drum brake linked by a cable to the door hinge, so when you open the door the drum is braked, though it isn't a strong brake.)
The soft suspension means that the Keymatic copes very well with unbalanced loads, the drum can be dancing around madly on spin but the cabinet will be still and quiet, with no vibration and even on its castor wheels, no wandering.
Several years ago when I lived in inner suburban Melbourne (Richmond) I owned several Keymatics I had collected from roadside hard garbage collections, plus some spare parts. When my partner and I were ready to move to the sticks, I had not yet discovered this great website and community, so I didn't really appreciate what I had and I disposed of most of it - a restored Keymatic I gave to the Salvation Army for a window display at a thrift shop, and the rest, I shudder to admit, went to the tip. I only kept a few spare parts. I had converted one to run from 12 volts DC, not automatic I must add, it used a Renault windscreen wiper motor for the wash and a small golf buggy motor for spin, plus a car heater fan motor to belt drive a Hoovermatic pump, plus 12 volt solenoids for water inlets and two clockwork timers, one for fill/wash and one for drain/spin. It worked really well and used hardly any power from my rudimentary solar power system at the time, but later I improved the solar power setup so I could use a regular washing machine and the poor old 12 volt Keymatic went to the tip, though I kept the parts to convert another.
Since then I have rescued another Keymatic, a Mark 4, but I can't restore it as the motor is missing. (about 15 to 20 years ago when Keymatics were being junked all around the country, people used to salvage the motor as a Keymatic motor/gearbox makes a good barbeque rotisserie motor for spit roasts.)
Chris