Center shocks do not work !!! It makes the for and aft too stiff give way too much steering. Play with different damper fluids first We have been using 100 weight silicone shock oil on rear and BRP 7460 on front king pins.
the best thing is to make sure that the t bar is free, and the pivot ball in not too tight. You want just alittle drag so you dont have any rear slop. Then make sure the front end is not bound up. Its amazing how much trouble that can cause. Then just 100 weight in the rear and silcone lube on the front will make a different.