Your tin plate attaches differently too. You will notice that the porcelain plate attaches directly to the computer, instead of the mounting brackets. I'm not sure which one was utilized first, but the porcelain plates will work, as they are the same length as the exposed part of your old tin plate.
You will notice at the bottom of your tin plate, that there is a line running across the front---well, there is a small tin piece missing there, and I think it was only for the purpose of closing up the gap and helping reflect the lighting.
There is a trim ring that goes around the sight glass, and can be purchased and installed on the porcelain plate if you desire?
I have the trim piece that attaches to the bottom, just not in photo.