The gearstick, more by luck than judgement, is situated at almost exactly the right location. The gearstick mechanism bolts to the gearbox by 2 nuts & bolts. If you want it perfect, you need to make a slot one of the bolt holes to allow the mechanism to move by about 5mm to centre the gearstick in the gear lever hole. Incidently, the reason you need to do this is because the hole isn’t entire central in the tunnel.
You should also completely remove the external reverse lockout mechanism. This is bulky and gets in the way. The gearbox has an internal lockout anyway so it’s not required. I suspect they only fitted it to standardize their range of cars.
I didn’t like the horrid Vauxhall standard gear knob however it appears to be bonded to the gearstick, so I removed the entire Omega gearstick and made a new one from various size bar and tube stock. This let me fine tune the length & fit a nicer looking gear knob.