MemcarDuino
That should be quite easy to integrate since there is already an Atmega2560 port available in the pull requests of the Github you linked.
Basically you just have to replace all the serial stuff with the SD stuff.
You can look at the SMS.ino file in the Cart_Reader folder to see what exactly is needed to add a new system to the Cart Reader project as the SMS.ino is the smallest file so far.
covered the inside where the battery
It could also be that Sketchup did an error when exporting, you can run the STL file through Meshmixer or Windows 10 3D Builder to automatically fix errors.
mx29gl128eht2i-90g Vender -ff6f id:7c00 7c00 Mario kart
Chip unknown - vender b0 id 000c 000c banjo tooie
Lh28f512bfnd-ptslzi - vendtr id 000c 000c res evil
I have stopped working on repro carts since it takes too much time. Basically you have to read the datasheet and compare it to the current code then make some changes and try if it works and then repeat until it actually works. It's not hard it just takes time.
I also have a Mario party 3in1 cart which i would like to dump, buts its larger then a standard card (2x512mbit!!!!!)
I guess you get the screen where you have to manually select the cart size, in this case just go into n64.ino and change the "cartSize = 64;" (line 1640) to 128 and see if it dumps the whole cart if not then you have to figure out how the mapper works in this Chinese multicart.