After an exciting exchange with Nick B. who has such a sharp sleuthing eye, here are some of our findings:
> The heart-shaped keys are most likely from an Underwood 21
> The paper table looks more like that of an L32, judging from the color. Nick, you are good!
> The red tab key is not from an L32 or any Olivetti for that matter, Nick noticed that it is not even flat
> Nick was right, voila, I found the red tab key to match that of the Rover 5000:
Compare this close-up of Gio's red tab
with the Rover's below.
I think it's practically solved. The mystery machine has a Lettera 22 body, a Lettera 32 paper table and label, the keys of an Underwood 21, and the red tab key of a Rover 5000!
Gio, it looks like you've got yourself a Frankentyper.