Based on what I've seen of the upper Empire A-arm, this is where I would start to add caster.
You may be tight on available adjustment on the heim joints. It will also require a recheck of the camber. As you move the front heim joint out (lengthen the heim joint out of the A-arm) it will move the upper ball joint rearward, but it will also tweak your camber.
So it will end up being a combination of constant checking both caster and camber, but there "should" be enough adjustment to get what they recommend. There is always the possibility that each frame is a bit different and you may have to settle for just 5 degrees of caster.
