Initial bodies
Deform base top to top piece using matching
Initial curves 
, target curves 
and
Fixed curves/edges/faces 
with None selected
for Match. The preview shows position
continuity matching.
Initial curves , target curves and
Fixed curves/edges/faces with Surface tangent selected
for Match. The preview shows tangent
continuity matching.
Surface tangent selected results
in a smooth, tangent continuity transition at the Target
curves