That Caddy looks great very unique . i'm no master fabricator like some but some flat stock and some added gusset should hold it still . Look at another build thread my track style T by J Robinson and also 3K build by Itoldyouso . They have done some great fabbing and you can get a general idea from them on shock mount building . Do you have the triangulated torsion bars to hold rearend center .

Look at some pics of a 4 bar rear link system at the lower shock mount . That design can be modded to lay flat and mount shocks also .