As you may have read, there were a lot of versions. Not all of them differed significantly from each other, but the story you’ve read is most definitely not the story I started with. Please join me in a quick tour of the versions that jumped out.
Before we embark on this epic journey, however, let me first advise you to keep an open mind, and don’t be sad if there is a version that seems far more awesome. Because there is. And maybe, someday, there will be again. I’m not done writing about Eddie, or the Accidental Universe.

The following will contain spoilers for the final version, and some minor spoilers for As Far As Souls Go.

Version 0
Not even the alpha readers saw this version. It never made it very far into story form to begin with. But the initial concept kicked ass.
After having been killed to death by Eddie, Toby would return for revenge, and I knew exactly how he’d get it. To that end, I started collecting pictures of hearses turned into hot rods, because Eddie was going to Race With The Devil*.
I had a pretty clear idea of how to write the fury and the flames, the gasoline fumes, and the rumbling engines. They’re familiar things, even to non-petrolheads, because it’s the kind of thing you see in a lot of movies. When you can somewhat rely on the reader’s imagination to do the heavy lifting, you can afford yourself some poetic wiggle room.
But there was a pretty significant issue: Toby’s dead. And not just soap-opera dead. If I wanted him back, I needed to have a way that at least sounded in line with the rules of the Universe. I couldn’t fudge my way out with a surprise twin, or something like that.
That’s what eventually killed the concept. Back to the drawing board.

Version 1
Pigeon coops.
The inciting incident for the next attempt was a pigeon coop. I wanted to write something so I went through the As Far As Souls Go characters to see if there was anything I could use, and I thought I found something.
We all remember Willie, right? Yeah, you do. Willie was fun, and so lovable that I had him reincarnated as a pigeon.
For the next trick, Eddie would find Willie in his new pigeon form, and after determining that this bird was in fact Birdman Willie, Eddie set out to build Willie a house. 
While the premise of a man building a pigeon coop is not quite strong enough to carry a book, it did originate the first element for the final book: Eddie went to a certain carpenter in May Valley.

Version 3
Based on plans for further books in the Accidental Universe, I decided I needed to build Eddie up more. To this end, I introduced a character named Ellerbie Pope, a documentarian who became interested in Eddie for some reason. Of course, you and I know the reason, but it wasn’t exactly public in Universe. Still, a problem I’d tackle later.
I knew Eddie needed to return to the Underworld, with this new character in tow, so somebody had to die. Not Rosalie. She died in the previous book, and she’s just not a damsel in distress.
Not the new character. He had to be there to witness Eddie doing his thing, and due to a fun scene with them driving to the Underworld, Eddie couldn’t die either.
That left just one person. Only Rooney was important enough for Eddie to break the rules again. Maybe the goths, but I couldn’t find a good place for them in the story, so they had to remain supporting cast.

Version 4 and 5
Next problem: How do we kill Rooney? Because it had to be spectacular. 
Enter Sam Hall, who didn’t actually have a name at the time, but he was a cowboy dressed in a white priest’s suit. And he drove a hot rod hearse.
The morning after a party at Jolene’s, Eddie wakes up and finds a banner with the first commandment of Helenism on the front of the church. He needs to show this to Rooney, and when Rooney steps on the road to get a better look, he gets run over by a hot rod hearse.

Version 6
All the awesome hotrodding was getting in the way of the story. After a while of trying to fit square pegs in round holes, I had to give up on the concept.
Back to square one. I had to ditch all the cool stuff… Do I even want to write this anymore?

Yeah, there’s something there. What’s left to work with? We’ll make something cool out of that…

One of the side stories from a previous version was the carpenter from May Valley being investigated by a group calling themselves the Current Day Saints. There had to be something there I could use. After all, Eddie returned from the dead. It already got the attention of some documentary guy, surely an organization like the CDS would have taken notice…
Luckily, at the end of As Far As Souls Go Helen goes to Las Vegas, which was supposed to be a story on its own. Still might be, but don’t hold your breath.
Herringwood Messiah begins after she’s been spotted there, and a CDS team is dispatched to look into Eddie and the church. This information was mostly contained in the prologue that’s been cut for pacing reasons. If you like, though, you can still read it. It’s available here, and you can download it in two useful formats.

*Musical Footnote!
As far as racing with the Devil goes, I know it’s originally by The Gun, but come on. How could I not pick the Priest cover? In fact, the The Gun version is only my third choice. Girl School also did a cover, and they’re friends with Motörhead, so if it’s good enough for Lemmy, it’s good enough for us.

There’s also a cover by a formation called High Heels, but they lose points because none of them are actually wearing high heels. I’ll give points back, plus extra, if the drummer is the only one who puts on a pair.