I wanted to mount mine inside the cab, yes it's possible it's difficult and the rods do need modifying slightly
First you will need 2 sets of the rods for the shifter one UJ a length of hollow bar that the internal diameter is the same as the external of the steady bar, then have to decide where in the cab you wont it

I put mine here so it doesn't hit my corsa dash.
The next thing was working out we're to drill the holes for the 2rods, we did this by measuring what angle the UJ worked at then setting the shifter at a similar anyle in relation to the rods under the car, we did this by having one person (me dad) under the car and lining it up by eye,

We then bit the bullet and drilled holes when we're both happy with there positions, we did shifter rod first and made sure it crossed paths with the one in the gear box

You then have to cut some off of them so that the 2 ends touch, then drill your UJ out so it's a snug fit
On both the shifter rods then drill through both the rods and the shifter on both sides of the UJ (gearbox side and car side ) to fit a roll pin)
With the other rod we turned the one attached to the gearbox upside down and mounted it on the gearbox attached the other one to the car to see how it looked, we need to bend the end up that was in the car on the gear box one so that it was at the same angle and ran on top of the shifter one, you then take the 2 steady bars and cut them down so there ends are touching then you take your hollow bar cut it down so it covers the join and abit either side and drill it and nock 2 roll pins in, I wouldn't advise welding the 2bits together as it won't fit through the hole on the floor lol
It will then look something like this


At this point we then decided to
Mount the bracket for the shifter so drilled to holes through the exhaust tunnel and bolted it down with some Polly mounts under it
Sorry don't have pics of that bit
Hope that helps
YetI