It may be a close fit, but there are ways around this.
The housing that holds the selector actually mounts on what you might consider calling the transmission tunnel that runs the length of the middle of the car.
I've just changed the selector on my 147 (didn't go short shift though) but I had to remove the exhaust cat converter and drop the exhaust rubbers / hangers for the rear of the exhaust to lower it. You also need to disconnect the handbrake cables.
You can then remove the rear cat hanger brackets and unbolt the big black solid metal transmission tunnel which will then drop the gear selector housing and handbrake out the bottom of the car, so make sure you've undone the gaitors up top at some point too!
You can then undo the 4 bolts that hold the selector housing to the tunnel plate. Depending upon what you're doing then you'll either need to remove the battery and battery tray to access the selector unit on the gearbox and undo the cables from it, or unclip the cables from the shifter housing and remove.
The selector housing looks like below and does run rather close to the big transmission tunnel plate. You can see from the image you should just have enough room to extend it by about half an inch. If you did run into clearance issues you could 'adjust' the transmission tunnel with an angle grinder or a hammer, to grant the clearance required but you'd need to weld a patch in if you did to stop the heat and road muck deteriorating the selector housing.
Image courtesy of AutoLusso - item available for sale on ebay.
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso
Last edited by Artermis; 08-06-15 at 04:45.