How do I go fullscreen with VirtualBox, keeping aspect ratio?

Question

I am running VirtualBox 5.1.30 on a Windows 8 host with a Windows 2000 guest with guest additions installed. The guest needs to run at 800x600, the host has a 16:9 display. I expect the person using the VM will go fullscreen.

When I go fullscreen normally, the guest resolution and aspect ratio is changed to match the new dimensions. I have tried using Scale Mode (Host + C), but the guest display is stretched to fit the aspect ratio of the new dimensions. I also tried going fullscreen, then manually setting the scale factor and resizing the virtual screen from the View menu. This gives close to the result I want, but when I restart the VM, the guest resolution reverts to the aspect ratio of the window.

The documentation says Scale Mode should do what I want, but this ticket suggests the feature might have been removed. How can I keep the guest resolution and aspect ratio when going fullscreen?

Answer 1

Somehow I missed that there is an option to disable auto resizing the guest display.

Disabling that, plus manually setting the scale factor works well enough for what I need, although it isn't perfect.