So when you say the other mount won't allow the boards to sit straight I assume you mean side to side since they are a spline mount & can sit roughly 360 degrees front to back. Does the rear mount have an adjustment for the tilt side to side?
I was looking at what Kuryakyn lists for the adapters & the one front mount 8826 looks like the rear one listed 8818 according to the installation instructions listed on their site. Was that one of the front mounts you tried that didn't work? It looks like it has the same set screw adjustment as the rear mount adapter.
Kuryakyn Splined Adapter Mounts
http://www.kuryakyn.com/Products/1598/Splined-Adapter-Mounts-for-Cruisers-Sport-Bikes