Here's what I found on the 66 Impala SS:
Impala SS engine options included the 250ci 155hp I-6, 283ci 195hp V-8, 283ci 4 bbl 220hp V-8, 327ci 4 bbl 275hp V-8, 396ci 4 bbl 325 V-8, 427ci 4 bbl 390hp V-8 and the 427ci 4 bbl 425hp V-8.
I imagine they were similar for the Impala as the SS package was cosmetic at that point.
P.G.