Rear drum brake can it cause high speed vibration?

[Bow Tie 67]

Update we verified that it had not lost a weight.

My buddy has a vibration which gets worse with speed. It's very bad over 100 mph. Its comming from the rear of the car. We noticed one of the brake drums has no weight on it. He thinks one may have come off during the restoration, but can't be sure if it was this drum. Is it possible this could be the cause? Or would a weight on the drum not be very noticable?

[Madspeed]

Id need so much more information its not funny

Hmm WTF do I even begin
you restored it ? Umm how many parts have been changed?
New dshaft? new U joints? Axles? wheels? tires? Pinnion angle?
u joint phasing? driveshaft balance? What engine? was it balanced correctly?
does it have the correct balancer and or flywheel/flexplate?
does it do it under full power Light power deccelleration. Neutral?
your better off to call me FFS cause I can go on for DAYS and my screen will run out of ink (lol)