Id be careful on poly bushes Martin. I was going to fit them (polysport ones), and even bought them ready to fit but i encountered three problems.
1. A VW garage that deals with my car said the poly bushes for the Golf GTis are a really tight fit. Because of this they can actually cause a bit of damage during the normal movement of the suspension parts to the point were they wear away the metal surrounding the bushes.
2. The garage said that no matter how hard they tried, they couldnt get them to fit. It was THAT tight.
3. Ive been told by a certain engine tuner, that the bushes ruin the feel of the Williams. So if you want to retain that original feel i wouldnt bother.
Standard bushes from Renault are cheap enough, and i noticed a massive handling improvement even with these fitted.