It was definitely a Cosworth build.
The owner of the car who I'm friends with on FB had a pretty good chat with me after the rally. I'm a little foggy on the exact details, but apparently the car was pre-owned by a gentleman who dumped nearly 100k into the car and had basically lost nearly everything to his wife in divorce, and put the car up on eBay for a quick sale. IIRC the current owner said he got it for around 20k? I'll see if I can dig up some pictures real quick and post them up.
Looking at the car, I have no problem believing it was a Cosworth build. He gave me a quick peek under the hood and I about pissed myself.