If I were you I would re-think the design of your front standard. I used a similar design on the first 5 x 4 camera I made, but instead of 0.5 inch wide aluminium I used 2 inch wide stock. Even so, the finished result was nowhere near rigid enough. I cut a slot in the base of the U, to give me cross slide, and this weakened the design so much you could rock the front of the camera back and forewards with only moderate pressure. Making a lens cap exposure could cause it to move...
For a 10 x 8 camera I would try to come up with something more rigid.
Alan Clark