Hi, those cylinders are simply connectors, so you should be able to disconnect them in the engine bay and inboard of the rear wheels. As Waylander says they carry the brake sensor and the ABS wiring (if fitted). If you have ABS, then I would not recommend you start chopping out the wiring! However, as you say they look like they have been disconnected, they are probably only the brake pad wear sensors.
Can you confirm if you have ABS in your car?
As far as the fitting of an S2 front is concerned, another forum member DarrylH did a great set of photos to show us all how he did it. I found the thread, scroll down to the bottom of the page:
http://forums.tipec.net/viewtopic.php?f=25&t=13151&start=870As you will see, some irreversible cutting is needed to the wings, but that is about all.
Advice for the fuel tank is sound, get as much fuel out as you can before you loosen the strap, as although the tank will not fall out (it has some mounting plates), it is plastic and the weight of the fuel will make it sag....it is then a pain to put the strap back on..

Hope all that helps!