Base height is definitely the go if you can get inserts to suit your application. I nearly adapted some S13 base height adjustable coilovers for better preload and corner weighing setup, but the majority of shock inserts would blow during a long rally stage. 36mm Bilstein inserts will do quite a few rallies between rebuilds. With a passenger of similar weight corner weights a less of an issue, and preload should be 'OK' if springs are at least captive.