@artifact you are right, from that image there is a fairly sharp edge. There is a shadow from there to the window to be mindful of. My approach here I think would be to take the edge you highlighted in green and extrude and scale down and adjust the shape of this extruded edge to match as best you can the shape of the window frame. If you find the window frame is too low @theluthier will be able to adjust to match your engine enclosure.
If you can save a file in the WIP folder on Google Drive, I will give you an example of what I mean.
As for files made in 2.8, they will be fine in 2.9. The issue comes when files made in 2.9 then opened in 2.8. So continue in 2.8 and you will be fine.
Strange though because I have less trouble opening the Dog file in 2.9.
