4.13? Do you mean 4.125 beetle gearbox ratio? It does not fit to bus box.
4,571 is the strongest ratio available to bus box.
3,875 is the strongest ratio available to beetle box.
They now have a 4.13 ring and pinion for the 091 bus box. I can't see why people would want to remove the 091 ring and pinion and replace it with this unit.
People have different needs and I dont know why other people need to understand. Some wants 1835cc engine, other 2L and next one 3,4L Pauter turbo engine...
You need ring and pinion. You need to know why and which one... Good luck!