Supercars Unlimited has a kit to allow installing a 1" rear sway bar with unboxed control arms. The kit has spacers to keep the control arms from collapsing. Has anyone had experience with this?

Beyond the control arm question, is a 1" rear sway bar overkill on a Cutlass?

 

probably will work OK, or they sell the piece to weld in into your LCAs to make them boxed

https://www.summitracing.com/parts/opg-rcai001

 

I LOVE my 1" rear bar - combines nicely with the 1-5/16 bar I installed up front - '72 cutlass ragtop, My rear bar is connected to UMI Performance tubular control arms but I'd expect similar handling performance when tied to OEM-style arms as well (not sure about the non-boxed idea, though...)

 

Just get boxed arms. The problem is that an open channel arm twists more than a boxed one. This twisting negates some of the added stiffness of the 1" rear bar, effectively making act like a smaller bar with boxed arms. If you plan to spend the money on an aftermarket bar, spend the extra $25 for the plates to box the lower arms.

 

You could also box your existing arms if you have a welder.