Your question implies that there was only one version of the 327. Actually the Corvette could have had any one of four engines, L75/300hp, L79/350,L76/365, and L84/375. The Impala engine, if original, would likely be the L75, so those would be the same. To get to the others, generally, would take a head, cam, and induction change, along with compression change for the two higher hp versions.