Got the ECU off eBay, actually. Not too many people looking for the grey-market 3.5 ECU & he didn't put a reserve on it, so I got it cheap.
At this point I'm happy collecting any (reasonably priced) 3.5 parts I can get my hands on. They're hard to find and I know I'll need them sooner or later.
Keep me up to date on your project. The way mine's going I'll be lucky to get it out on the road next summer...