I totally read the part of his post stating he did the Wilwood front disc conversion and where used these adapters on the rear and wasn't thinking that the rear end is probably still the small bolt pattern, hence the need for them out back. Guess I kept thinking they were bolt on spacers and not the bolt pattern adapters. (I didn't even think about the Torq Thrust 2 is available in 5x4.5 or the GM 5x4.75 bolt pattern but not in the small 5x4 pattern.) I went through this a few years back on my '72 Duster when I converted the front from the 9 in drum to the factory '73-76 disc setup. My car already had a lbp rear end in it so I simply didn't think about it.
Still, these spacers / adapters shouldn't be working loose if torqued properly... unless there is another issue. Brake drum not seating on the axle flange from rust or debris, warped drum, warped spacer, poorly balanced tire, etc. Could try putting the rear end on jack stands withe the adapters bolted on without the wheels bolted up and have a helper put the car in gear and allow the axle to spin slowly. This would be an easy way to check for and obvious visual issues with warped parts / runout that could cause a bad vibration. It may help guide the owner in the right direction.
