If you're into this, you'll love M539 restorations. Here's a ground up rebuild of the S65 V8 out of an E92 M3: https://www.youtube.com/watch?v=NfuXp8QnWoU&t=2s
This is insanely expensive amount of parts in this video, not even counting the work itself. Basically it would never make economic sense to do a rebuild like this.
- Crashed in the US - Auctioned to a European dealership who replaced the odometer - Sold to two more owners, the latter who seized the engine
He's traveling around central Europe to tow cars from people who would otherwise scrap them.