I have not. Got these MII used with orange front, red back. It’s a decent setup, but I’m getting some wobble around ~32mph and I’d love to gain some more stability. Turning is actually great, so I’m not sure I need to mess with the front.
But to be honest, i only halfway understand truck angles, bushings, and all the combined effects.
You’d actually get less stability with softer bushings in the rear, especially since you will have created essentially a symmetric setup. I’d try the preload first, possibly even in the rear as well as the front.
Although don’t forget to blue loctite those retaining screws. One worked itself loose while riding and the bushing fell out during a turn.
If you’re in Ohio I have a bomb of a battery that may be salvageable with a bit of work. Zero liability on my end tho, you burn down your house & it’s on you