XR4 Gearbox IB5+ Issues

[Diddi]

Hi, recently purchased a 2008 WQ XR4 for my daughter as she wanted to learn to drive in a manual.

Joined this forum hoping to get some information on gearbox options. Gearbox jumps out of 2nd gear when decelerating and crunches when going into 3rd. Gearbox oil replaced with Penrite PRO GEAR 75W-90 Full Synthetic, which did improve the 3rd gear crunch somewhat.

The only alternative appears to be the MTX75 gearbox, but have not been able to find a kit to facilitate/enable the swap out, and it appears some of the frame has to be cut away to fit the MTX75, so I'm not sure how I'd go in regards to engineering certification.

It appears the only other options are a sequential IB5+ out of England, which would probably cost more than what I paid for the car, or have the current unit rebuilt.

Q1) Is there any other workable and stronger alternative to replace the IB5+?

Q2) Can the IB5+ gearbox be built stronger, and if so what are the parts I need and where can I purchase them from?

Q3) Apparently the diff is a weak point. Recommendations for a good quality replacement Limited Slip Diff which would improve handling?
I'm not sure if the information is correct, but I have been told some LSD's can turn a FWD vehicle into an under-steering pig.

Q4) Recommendations for someone who can rebuild the IB5+ stronger? I'm in Tamworth NSW and would be happy to drive as far as somewhere like Newcastle, or alternatively have the box removed and shipped to whoever does the rebuild best.

The XR4 is great little car and reminds me in many ways of my Mini Cooper S when I was a teenager. It would be great if I could sort it for her.