as the topic has changed from “what is the VIN of the donor car” to “how hard is it to replace an S2 engine by an S3 HE”, I thought it would be more relevant to open a new topic here :
https://forums.jag-lovers.com/t/how-hard-is-replacing-an-xj-v12-series-2-engine-by-a-series-3-he/433268