It might not be very likely, that one has to replace a VIC-20 cartridge guide, except it got really rusty. The more likely use for this design is the VIC-20 replica VickyTenty. The cartrdige guide is not mandatory, but if you don't have one, you will soon want one, because the cartridge guide will let the cartridge slide in place more easily and it will also stop the cartridge from falling into the case. And it keeps the power LED cable out of the way.
VIC-20 cartridge guide on a VickyTwenty board
The design is actually petty plain, but I had to discard a couple of prints/attempts, because of layer adhesion issues. Originally, there were four screws through the board, that held the cartridge guide, but the material was so thin, that the screws slightly broke the print, since the drills are parallel to the layers.
Original design with four screws
The two screw holes in the front could not have a thicker material, since this would habe been collided with the cartridge. The holes in the back are beside(behind the cartridge connector, so the material could have been made wider to make cracking less likely. The front screws have been replaced with hooks.
Final design with two hooks and two screws
Nevertheless, it is helpful to widen the screw holdes with a 1.8mm drill bit. I am using 2.2mm x 6.5mm (self taping) screws for sheet metal (C 2,2x6,5H, DIN 7981).
Find the project data on thingiverse.com: https://www.thingiverse.com/thing:5230393