I had a similar issue on my 4be after a replacement tyre was fitted. It felt like a wheel balance problem, with the wobble occurring at about 50-60 mph (buckled wheel tends to be about 70-80). The balance weights were still there so I took the wheel off and found the spigot ring was missing. A wheel will only need a spigot ring if the wheel centre hole is bigger than the spigot on the hub. You can't rely on the wheel nuts/studs holding the wheel concentric to the hub if the hole doesn't match the hub. Whip the wheel off and have a look at the relevant diameters.