Mark,
Do you have a knocking noise as well as the visual wobble, especially when the steering is on lock? If it is not something simple like loose wheel nuts, bent rim, etc, then it could be a wheel bearing loose or collapsed, or a tracta joint that is siezing. Drive it around on lock, and listen for noises. When a joint has got a sieze, it semi welds to the other part, ending with a hole on one and a pimple on the other part, if the joint is moved of the normal line of drive to say a slight lock, then the pimple will ride out of the hole and the shaft rotation can be "notchy", ........a possible cause.
I worked on Foxs (along with all the other vehicles that Her Majesty had), from when they entered service around 1975 to there demise around 1994.
Richard