If it's running like that at high speed then I'll ask if the transom is sharp? If not, it'll suck the tail of the float down and you'll never get on step. That's why some boats have adjustable trims attached to the transom. Maybe your float does not rise after the step? the cunningham article showed 3 degrees rise, both before and after the step.
You gotta get the nose level and get the tails of the floats out of the water so you can build up flying speed. Even if you have to hold DOWN elevator at the start of the run. You COULD try that, just bump a little bit of down quickly to get the tails of the floats free of the water.
Your thrust lines of the motors don't look to be excessively weird. Huge amount of up-thrust could 'splain what's going on.
8 pounds with (2) .25s does not sound out of bounds but a little on the heavy side. Certainly one .25 will fly 4 pounds... Your problem is not weight-yet. You have some other problem with getting the floats up on top of the water. If it's too heavy it will be sluggish after it's airborne.
KiwiKid's remark about the float in front of the prop is good. Ususally 20-25% of the prop diameter in front of the prop is about right. If you have a lot too much float too far forward it can make the plane laterally unstable in the air.