Added a vertically oriented top case as per my suggestion below, I think this one would produce best print quality and also requires no support if printed with Cura's adaptive layers. I'm printing one using .2mm layer 100% infill.

The ZX81 was my first computer, many hours were spent playing games like 3d Monster Maze and others, and typing in games from magazines then losing it all due to ram pack wobble, but it still holds a place in my heart that I just can't let die.

I'm currently repairing a few old computers and needed a case for an orphan ZX81 board (pictured) that I was given a few years ago.

However I could not find a replacement case, so I modelled one from scratch over the weekend.

For best print quality, I think the bottom should be printed as supplied, but the top may look better if printed vertically with the back on the build plate. supports should not be needed if printed in this orientation,
However you will need good bed adhesion.
If you are printing the case top on a machine with a moving y-axis, orient the model so the model is aligned in the y-axis not x-axis as the y-axis movements may cause wobble as the printing nears the top.
Cura has an option to select face to orient with build plate, so it should be easy to set up.

The screw holes in the bottom have been made to fit the feet that I have included.

I welcome any constructive comments to refine this model if any adjustments need to be made.