I've just paid £150 for a very good condition RS1600i set up, which is better than the Series 1 if you can get hold of one. As said though you need to use a MK3 or 5 gearbox casing as they use a brace not a cradle. I'm goign to see if I can modify the RS1600i set up to use an S2 box and cradle though.
Think you will struggle getting the tension strut past the crossmember.
Its only the end casing on the box that needs changing for the different mounting legs.