Aluminum is fine, just recheck the bolts after a week or so. Aluminum will settle some where steel won't. Since the part is in compression it's not going to fail. Aluminum is WAY easier to machine than steel so if you are making them or having them made it will probably cost a lot less.

You do gain over all travel because the a-arms are now farther apart. That extra inch you spaced the spindle and lower arm down is an axtra inch of compression travel.

The geometry will remain the same as long as the ball joint is lined up with the hole to which it mounts. Actually, it would be harder to make it misalign that it will be to align it as you have to thread the spacer top and bottem, etc... Not that being able to space out both joints (upper and lower) wouldn't be something to try but it would require some healy machining. It would effectively give you longer a-arms.

As for the arcs, they are determined by the pivots on the bushings. Sure it will be a little different, and I mean a little because we are only talking a inch, but what matters is your tires are properly aligned at rest. The way it is now the camber and toe change as they swing through the travel. With the spacer your tires will lean ever so lightly more inward (the lower arm will swing out a bit more initially) when cornering which is good. Since the tie rod is located close to the plane of the upper ball joint, it will not be effected much if at all by the spacer. (again, it only matters when you flex because as it is your toe goes out when the suspension flexes so guess what, with the spacer it will still go out <img src="/forums/images/graemlins/grin.gif" alt="" />)

Adding the low pro stops to this kit could yield what, 8, maybe 9 inches of travel? I'm not sure what you get stock with low pros but you can add an inch to it with this.

Frank.