I would graft shipmaku for a few reasons. To me the foliage is much more desirable, particularly that of the kishu shimpaku, which I have been propagating for the last few years. So whips for approach grafts or, buds for bud grafting are readily available to me.
Second, it would solve my issues waiting for the tree to backbud in certain places. I could graft on foliage to existing branches, exactly where I would like it. The left side of this tree uses fore shortening extensively, because the foliage is so far from the trunk. I think to some degree this looks un-natural, but it allowed me to style the tree, while waiting for back buds, and existing buds to grow out to replace the twisted up branches.
Thirdly, I personally don't care for procumbens at all, ( even though they make up a fair amount of my collection). I feel that with shimpaku, I could end up with a much more refined and visually appealling tree.