OK. Difference between S1 and S2 is the fuse box. In the S2 it is a much grander affair and, on the face of it, much better engineered affair. Unfortunately There are two serious problems with it. First it is easy to fit the incorrect fuses which are slightly shorter than the originals. Then there isn't enough contact between the fuse and holder and everything overheats. Second the looms seem not to have been properly put together and the wire to fuse terminal crimp is frequently not tight enough. Overheating then ensues. Then the plastic of the fuse box base is extremely susceptible to heat and will even burn at very low temperatures. Net result is that S2 fuse boxes rarely deliver full voltage to their headlights!
The S1 and the first 18 months production of S2 has a dear old fashioned Lucas 4 fuse hangover from the fifties that is far more robust.
Will these lamps on Ebay improve your forward vision? Probably. Quality of forward vision is driven by three things - wattage/quality of the bulb; quality of the reflector/lense; adjustment of the lamps. The Ebay ones allow the required bulb upgrade but are an unknown quantity on quality of reflector and lens. Personally I'm a huge fan of Cibie, having been brought up on road rallying where they reigned supreme.
This time of year is a gift for making sure you have got your lamp adjustment right. Just go out and find a nice quiet spot on a fooggy night. You'll be able to see exactly where each lamp is pointing. Mask/unplug any that are confusing your analysis. Then you can set them up exactly right! Far more efective than all this laser rubbish they use in gagrages!
Chris