It's always exciting to hear about updates on the Touring, and I'm glad to know you're still driving and enjoying it. The original build thread was a huge inspiration to me and one of the reasons why I got my own red RWD touring a few years ago to convert to a ZHP. If you've got more info on its current state and the S54 swap you should definitely start a new thread.
Bummer that the rust has continued to grow, but it doesn't sound unfixable at this point. It's a truly rare and special car as I'm sure you are aware. Basically 1 of 1 spec once you start digging down into the nitty gritty of the options.
On E46 Fanatics we've been working on a spreadsheet to figure out all the North American touring production numbers, and do a complete option breakdown of every car.
Total production was around 20,500 cars, and VIN code EZ15XXX is for the facelift (2002-2005) tourings w/ RWD and manual transmission. This was the first group we've run through mdecoder to capture all the option content. There were only 738 cars of this spec built of the 754 shown in that range of VINs.
Breaking down that range even further in the spreadsheet, EZ15717 was one of only 10 built with gloss shadowline trim, and the only one of those that was Japanrot.
