On one of my 7's I never had the problem until I recently changed tyres and then got the 50/60mph wobble. Went back to the tyre place and they said it was within tolerances and the best they could do with placing weights 'out of sight' on the inside of the wheels. He then got them balanced fully using weights on the inside as well and problem was solved.
My car has many new steering/suspension parts as well so seems we're susceptible to small wheel alignment issues.
Cheers Paul,
1976 TR7 2.0 FHC, ACG 3115 - Java Green (on the road)
1976 TR7 2.0 FHC, ACG 2367 - Carmine Red (on the road)
1980 TR7V8 3.9 DHC, Orient Blue (on the road)
1977 TR7V8 4.0 FHC rally car, ACG 35005 - Tahiti Blue (complete, no MOT)
www.TR7.co.uk