Teahead, that's a great conversion as well, but it's an S38.
With the price of S38s skyrocketing, and the availability of parts for them becoming an issue, I decided to go with an S54 for my E9. I'm working with a fabricator that has a great deal of experience with S54 conversions. But be warned, you'll have to get rid of the E9 steering box, and probably the front suspension. But there should be bolt-on solutions for that too.
You'll be able to buy the parts straight from the fabricator, and I'm doing a full DIY build thread. Hope to have something to show you in the next few weeks.