I think mine is a bit different - The parts where I'd be cutting, from memory, would be thicker than 15mm diameter, meaning the sleeving tube would need to be larger. Given that its already close to the upright, this might be a problem.
Should I consider buying something like the column in this link:
http://www.ebay.co.uk/itm/FORD-SIERR...item46121076b4