Skids - as far as I can see, the earlier 900ssie arm is the same as 800 and 900 Sport steel arm. And 5 spoke wheels fit them cos my 800 Sport road bike is thus equipped atm (although not for much longer).
Find some S4 wheels - I've seen S4 wheels pop up on eBay regularly and Jim at Bike Enders has them in from time to time too. 900S, 800S 750ssie 3 spokes (although the 750 rear is a 4.5" rim) will also fit because I used them for a while until I got some more 5 spokers.
http://www.twpd.co.uk/pictures/800ss250306-1.jpg Phil - does your bike have the underslung rear caliper?