Steering wheel/front vibrate when braking at highway speed

1970 Plymouth Duster, power steering, drums all around. This only happens when applying the brakes at highway speed. I passed inspection in Sweden previous summer. My brakes were was very nice and even. Some play in the idler arm even though it was brand new at that point. Maybe the header kills it quick? No other play in linkages, spindles etc in the front. They shake the car quite good to make sure during an inspection. I adjusted the power steering adjuster and it made the vibration in the steering wheel better, but I still feel the vibration in the front. I have 14" wolfrace wheels on the car. I suppose it could be the drums, it could be the idler arm maybe? Any ideas?