I use those Tubus clamps you linked to and they are a very well engineered solution; however I strongly recommend that you use a one piece front rack, with an over-the-wheel rod. This adds another bracing component to the system and reduces the rotational force the clamps will be subjected to. I would not be comfortable with using the clamps with the rack you chose. That rack also does not have a mechanism for adjusting levelness, like the one below does.

Old Man Mountain AC Lowrider: