1881? That is one old
Trillium :-)
I'm in the process of doing the same Brenda. I picked up some larger new but older style hatches on ebay. The older style have square corners and you can remove the screws and cut them down to the exact size you want. The style matches the
windows. I plan on using the
fiberglass I cut out in the hatch door itself.
If you are in or passing through the GTA you are welcome to come have a look. I'm not far from the 400/401 interchange.
Double check your measurements, what you see on the outside may not be what is available on the inside. And the body/floor slopes in that area. I used 2 people - 1 inside and 1 outside with strong magnets to determine the limits of the opening.