To add to Jerry's comment on "oversprung", it'll knock your teeth out!

I don't have a vision of your stock shock mounting so I may not understand the issue. Typically, if you raised the axle with the lowering blocks, and the shocks mount to the bottom plate that clamps the spring (similar to the Speedway piece you referenced) the relationship of the lower and upper mounts would remain the same as original, so the shock length shouldn't need to be changed. If the shocks mount to the axle housing instead, then the raised upper mounting points as Jerry suggested would be the better choice. The one point I would make is the strength of the upper mount could be important if there ever were the chance for the shock bottoming out.