A quick remix of the fantastic adapter by Athakaspen. I just added a hole on the back to easily push the cart back out of the adapter without additional tools.
The square cut adapter is from an earlier variant of the print, I've moved the hole higher to completely cover the cartridge pins. There are two variants of the model included. one has a rectangular hole like in the photo, the second is a round hole which looks a lot nicer. I thought it would be more fragile but after printing it I think it's actually sturdier.
Print this with the thinnest layers you can. My first print I ran it at my printers "standard" layer resolution, and the backing of the cart was only one layer thick. My second print I did at the thinnest my layers print and it came out much sturdier.
I just edited this really quick in tinkercad.