I have never removed any gears from a transfer box, but to do it you would need to remove the transfer box from the car which I have done to access the starter motor. Below is an copy and paste from a post I placed on another forum. Again just ignore any reference to a starter motor and I assume in 2wd you wouldn't need to refit the prop shaft. As you can see it is reasonably involved.
Disconnect the battery connections
Jack up the whole vehicle and place on axle stands, I used 4 stands to lift the whole car. You need to ensure the car is safely supported as you will be working underneath.
Remove the engine under shield.
Drain the gearbox and transfer box oils, as the car was on my drive I didn't want any major oil spills, this proved essential in my case. I did this later in my process and wished I had done earlier.
Remove the 4 bolts securing the underside chassis brace. needed to remove the exhaust.
Remove the exhaust, 3 bolts at the engine. I removed the whole exhaust as the centre bolts were badly corroded, just pop off the rubber mountings.
Remove the prop shaft, don't hang the prop shaft on the front universal joint as it can be damaged.
Under the bonnet loosen the 3 nuts to the RHS front suspension strut approx 5mm, no not remove them, ensure they are still wound onto the threads.
Remove the front RHS wheel, remove the strut cable bracket, remove the two nuts at the bottom of the strut and knock them out whilst supporting the hub, under the car knock the drive shaft off the RHS transfer box splines. I left one bolt in the bottom strut hole to the top hub hole to support the hub.
Remove the transfer box support bracket by the RHS front wheel where the drive shaft is located. 5 bolts.
Remove the rear engine mounting bolt above and behind the transfer box. I found I didn't need to re-support the engine but check before you remove this bolt, good idea to support the engine whilst this bolt is removed then gradually remove the support checking the engine is supported by the front and rear engine mountings.
Remove the two bottom transfer box bolts to the gearbox.
Remove the rear mounting bracket bolts 3 are M12, 2 are M10. One is bolted into the engine, the others are either through or into the transfer box. I found it easier to access 4 of the bolts from the RHS removed front wheel and the engine bolt underneath. Mark where the bolts came from as they are all different, The engine bolt is inside the bracket and difficult to access. Bolts are either 15mm or 18mm heads.
With the mounting bracket loose you need to lift the mounting bracket clear of the top of the transfer box, this is awkward, you need to flex the harness cable above slightly to create clearance.
With the bracket clear you can slide the transfer box towards the RHS front wheel to clear the gear box then lower out of the car. Beware you get oil spillage and at this point you realise what a good idea it was to drain the transfer and gear box oils.
The starter motor bolts and power connectors can now be accessed.
Reassembly is the reverse taking the following into account.
The manual recommends replacing the O Ring on the transfer box to gearbox shaft, this was available from Vauxhall approx £7.
The manual recommends the mounting bracket bolts are torqued to 90NM, I did this and stripped the M10 thread into the top gearbox mounting, requiring a helicoil repair, so be careful the manual can be misleading. This did my bolts to the following torques, guided by the manual. At your own risk, please consider this is my opinion only.
M12 Main rear rubber mounting bolt 90nm
M12 lower 2 bolts to mounting bracket 90nm
M12 upper single bolt to mounting bracket 75nm
Two M12 lower transfer box bolts 75NM (underside of transfer box)
M10 Bracket Engine bolt and top transfer box to bracket bolt 60nm
M10 5 bolts to transfer box support bracket by the RHS front wheel 60nm
Rear prop shaft bolts 50nm, centre and front prop shaft bolts 25nm
When rebuilding I did all the main transfer box and mounting bracket bolts up lightly before finally torquing up.
Its a good idea to grease the engine undershield bolts before you put them back in, it stops them corroding.
I used EP75-90 gearbox oil for both gearbox and transfer box. I put 2.4 litres of oil in the gearbox and fill the transfer box to the fill plug (approx 0.8 litres).
I needed to replace the gasket on the exhaust flexible connection.