Easiest fix is of course to swap in another complete 220 axle. An Amazon saloon one can be used if you convert it to Wagon style tabs for the suspension arms. There used to be a kit available to do that. I've never heard of a Wagon using a limited slip diff. I have a Wagon too here in the UK. Unless you drive in adverse conditions regularly where you need the added traction I don't see the need for it. Easier to put some Mud & Snows on the rear when needed, or studded tyres if that is legal where you are. Converting the Wagon axle to a 4.10 ratio has always been a problem but adding overdrive is good and gives you the same gears as the 123GT, for example, or any other Amazon with OD as standard.