If you are set on
ATS then I would buy
these and source the control arms and coilovers of your choice directly. You will need to get on the waiting list for the Tall AFX spindles....or do the G-Mod yourself and use stock height spindles. Tyler is really hard to get ahold of right now.
Or, call
DSE and do the one stop shopping deal. The nice thing about their c/o conversion is that it corrects the geometry with new upper control arm mounts...this allows you to use a stock height spindle weather it be a GM spindle or an ATS AFX (stock height).
Another great option is
Speed Tech they have great parts and pricing.
Do your homework, you have options!