Huh?!?!?!
1) S15 Silvia had the same body construction as the S14 Silvia, which had the same body construction as the S14 240SX, which is a unibody STEEL frame with STEEL panels.
2) The S15 Silvia had McPherson struts up front with a multilink suspension in the back. Yes, the design in the back is similar to the Skyline, but if you want to compare the Silvia's suspension is more shared with the Z32 (Fairlady/300ZX) than the Skyline's (which uses multilink at all four corners).
-alex