Buy from a chassis builder that can supply you with the set up brackets. I’ve been under enough 4 link cars that werent built correctly for ride height/ bracket angle.
The relationship between the two brackets, ride height, and chassis placement is much harder to screw up if the 4 link brackets are installed using set up brackets during the build.
Set up brackets bolt into the front and rear 4 link brackets instead of the individual bars. This ensures the relationship of the front to rear brackets stay in a position that allows the bars to be placed in any hole without major adjustments when the chassis is finished. Without set up brackets, true placement in the car and on the axle is difficult to get perfect.