Gavanized Steel Waste Pipe

[pinkmonkey]

good morning all,

I am a newby to this forum but consider myself a relatively experienced (read old) DIYer. 

I am currently helping my son to renovate his first flat and we have stumbled at the first hurdle. We are installing a new bathroom and he bought a nice little close coupled low level loo from Victoria Plumbing. However, after ripping the old loo out we discovered the soil pipe is slightly in the wrong angle and height. Also the loo needs to go right up against the wall and in that position the soil pipe would be slightly too far forward. So my grand plan was to install a new soil pipe at right height and angle. However, when we uncovered everything we found that the soil pipe appears to be galvanized steel with no seams other then welds and this fits directly to the main down pipe (stack) for the building (6 flats). 

I have never come across this before and dont know how to tackle it. See the attached pics which show the pipe. Can I cut this pipe? I assume with a disc cutter, or is this going to cause more problems. Its seems a fair bit bigger than normal pipe, I havent measured but I am guess its 150mm internal. 

A secondary issue, is that in the pic you can also see a old style 32mm copper drain pipe from the sink runs across the back wall. This is also in the way of the toilet cistern so need to move this. My thoughts are to fit a new soil pipe with a vanity outlet and replumb down to the soil pipe. Anyone see any issues with this? It all hinges on that flaming soil pipe. 

The only other option (fallback) is to let sleeping dogs lie and leave the soil pipe along and just box in the back and move the toilet forward and then use an extension to the old sild pipe. Once again not sure if they do this odd fittings. Any help appreciated. 

Edited February 26 by pinkmonkey