ah just seen your new pics. Yes 8P is just a normal 1.3 litre 5-speed polo gearbox. Not worth much at all. You can find these for sale for not a lot. They are the usual box to put on a g40 if the original ATV coded box is shat itself and you can't find a proper replacement. The ratios are similar but not quite the same, about as close as you'll get. Top end is a bit compromised and I'm not sure it'll do 60 in 2nd with an 8P (which it will do with an ATV).
Also, you can't fit an LSD to an 8P as they don't have bolt-on crownwheels on the diff.
But you've been using an 8P anyway so using another one shouldn't be a problem, it'll just be the same.