The advantage of fitting dropped spindles is that you can go lower without reaching the limits of travel on the ball joints. The red9 coilover kit just replaces your normal suspension leaves with coilovers in the place of where you shock absorbers currently are. It is also up for debate as to whether the mounting points for the shock absorber are actually strong enough to take the full weight of the bus when using them for coilovers alone.
Most would recommend a combination of dropped spindles and aftermarket coilovers, but retain the standard suspension leaves. This means you get the advantage of your ball joints are at less risk of bottoming out, the coilovers not having all their weight put onto the mounts, but they still offer you a degree of ride height adjustment. Coupled with an adjustable beam, and you have a lot of options for changing the height.
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