I don't know the bumper, but Hi-Lift does make a bumper lift accessory for the high lift.

Either way, like the laster said, never get under a vehicle unless it's supported by jack stands.

You can lift the truck with the hi-lift and then put jack stands under it and you'll be fine, just make sure it's a fairly level surface.

I quit using my floor jack for the X as I need to block it to get the wheels off the ground. I now use the hi-lift on the sliders and jack stands.