These are 45 degree angled mounting platforms to display your 8 stud wide LEGO Speed Champions, the mounting plate hooks into the chassis pieces with 4 studs, I made a modified version for the 1970 Ferrari 512M, see the 4stud file for that one.
I have added a new version for the updated 2023 chassis piece, not yet tested.
Printing wise it worked best for me with the studs angled downwards and small supports to stabilize their lower edges (see pictures).
Hope you like it, and I might update more specialized versions down the line if needed :)