The oil in the tailpipe will be around even after 3 weeks if it's burning oil. Problem with that is it the rings that are bad or the valve and seals. Could be both.
I wanted to mention it weird that the engine just failed. There are two special diamond coated washers that go on the outside of the crank sprocket. That is what holds the crank timing together without the keyway. They could fail after so many miles.
The duratec engine is used in many ford vehicles. It's the same motor being used in the new four cylinder mustangs. Its great design. The bottom end is solid. The head has 4 valves per cylinder. It has a light weight valve train and solid lifters. With a turbo these motor look like they can kick butt.
I believe they came out in 2001 for the Ranger but they seemed to be in a lot of the cars in Europe. Check out this site: SBD Motorsport - Fast Ford Duratec Tuning
or this one http://www.cosworth.com/products/cra...ratec-engines/
. If it wasn't just a Ranger I might beef up this motor and have fun with.