I believe the most major change vas the inclusion of LCD MFDs for most instruments in the cockpit if im not wrong and small upgrade in avionics and the rails to accomondate the more modern missiles.
Only the JA-37D, AJS-37, AJSF-37 AND AJSH-37 had Gripen parts as far as i'm aware when they were still waiting for JAS-39 since it was delayed and ALL or most 37 models before that didnt have any JAS-39 parts.