This it the parts list for conversion of a 1.8 16v to a Williams wide track suspension setup.. Parts price are a alittle old but give you a good idea.
Springs:
You can use williams springs, 172 springs or clio 1.8 16v springs - I won't list OE part numbers for these as they are dependant on a coloured spot on the original items. Aftermarket wise you can fit any lowering springs designed for a williams or clio 1.8 16v or, alternatively, you can fit coilovers (see below). Stock springs are 125lb and from a 172 full fat.
Front Shock Absorbers:
77 00 838 095 - Williams front shock absorber (40.67 each)
77 00 838 095 - Williams front shock absorber (40.67 each)
You could obviously also fit aftermarket shocks or coilovers - however, these must be designed for a williams. SInce hubs are the same on valver and Williams only the shocks give the different track.
Wishbones:
60 01 025 842 - Williams wishbone - right hand side (48.30)
60 01 025 841 - Williams wishbone - left hand side (48.30)
Renault 19 16v wishbones will also fit.
Anti Roll Bar:
60 01 025 814 - Williams ARB (72.11)
Renault 19 16v ARB will also fit, as will some megane 1 ARB's (IIRC its the non-16v and non-coupe one you'll be after)
Anti Roll Bar Fixing (At Middle):
77 00 785 788 - ARB Bush (5.49)
77 00 785 788 - ARB Bush (5.49)
82 00 078 548 - ARB Clip (2.75)
82 00 078 548 - ARB Clip (2.75)
77 03 035 027 - Nut (0.73)
77 03 035 027 - Nut (0.73)
77 03 002 116 - Screw M8-2 (0.69)
77 03 002 116 - Screw M8-2 (0.69)
These items are not really necessary as you will be able to use the 1.8 items but IMO it's worth doing as your original bushes could be quite worn dependant on age/milage of your car.
Anti Roll Bar Fixing (At Wishbones):
77 00 784 170 - ARB Bush (5.49)
77 00 784 170 - ARB Bush (5.49)
77 00 784 169 - ARB Clip (3.61)
77 00 784 169 - ARB Clip (3.61)
77 03 002 116 - Screw M8-2 (0.69)
77 03 002 116 - Screw M8-2 (0.69)
77 03 034 017 - Nut (0.36)
77 03 034 017 - Nut (0.36)
These items are necessary to mate the ARB to the wishbones - the 1.8 setup mounts differently so you cannot use your existing components here.
Driveshafts:
77 01 367 623 - Williams driveshaft - right hand side (156.19)
77 01 367 627 - Williams driveshaft - left hand side (156.19)
Depending on if you car has ABS you may also need an ABS toothed ring for each shaft. It may be possible to salvage these from your 1.8 setup but if not then the part number is 77 00 867 344 (14.23) - you would need two of these if applicable. It is also possible to substitle the passenger side driveshaft with a R19 16v item.
Also try ringing round comapnys who make driveshafts I got mine from a motor garage for a lot less than Renault and it a new not refurb part just took a few days to get to made up. However be careful they they don't sell you the valver shafts Halfords etc order Williams ones in but they turn out to bee the same part from a Valver and won't fit.
General Notes:
If you get asked for an oval plate number (i.e when ordering driveshafts etc) you can use 'C57M' which is for a Williams. If going for alternative parts (i.e. R19 16V) then you would need the corresponding oval plate.
Also, going for all new parts will cost quite a lot so i'd try and source some of the parts secondhand.