One of my rear upper control arms has a small reinforcement welded to it on the end that goes on the rear end housing. Unfortunately, I did not notice this until they were off and mixed up. Anyone know which side the reinforced arm goes on? Thanks for the input.

Driver's Side.

i thought the control arms were unversial

On a 12 Bolt equipped Chevelle, the Driver's Side Upper Control Arm is reinforced and ground for clearance purposes. On 10 Bolt Rear Chevelles, the Upper Control Arms are interchangeable.

http://leverfamilysite.com/Create_12_Bolt_Arms_From_10_Bolt_Arms.htm

Thanks for the help.