I had the same on my cortina changed complete front end,arms,bushes,subframe,stub axels,bearings,tyres,wheel nuts,shocks only to find out that my wheels were the wrong offset and increased my track by 10mm overall these wheels were et 35 and i changed to et 40 problem gone!!!!!

may be worth trying a mates front wheels, et 35 is standard cos offset.

hope this helps

my wobble was at 40 to 50 mph