[DW31S]

It is a VERY nice car, however, it is not a factory assembled W-31. The car is well known in the Oldsmobile world, especially among the W-31 fans. The truth came out when it was at MCACN a few years ago; the savvy Olds guys knew before that. The eBay wording is nefarious and never claims to be a genuine car. There is another claimed '69 W-31 floating around that has also duped some people, especially the folks at Hemmings when it was awarded Muscle car of the Year in 2008. Without bulletproof docs, W-31s are somewhat easy to create and can fool even some of the best car people. The Oldsmobile P-O-P doesn't list pertinent info like others, so having one, while helpful with some info., isn't a way to authenticate a car or drivetrain. The longblock and intake on a standard '69 350/310 will look IDENTICAL to a genuine W-31 engine, so the "Numbers Matching" or "Original Engine" could very well be true. The W-31 specific camshaft, pistons and valves are NOT visible unless the engine is taken apart, so creating the illusion by adding the correct 7029255 Q-Jet and thicker harmonic balancer isn't terribly hard other than being expensive. Even the exhaust manifolds and distributor that are used on the 325 horse W-31 will carry the same numbers as the 310 horse version. The automatic transmissions used in the factory-built W-31s are different that the pedestrian Turbo 350 and the eBay listing has some clever words to disguise the fact the trans currently in that car wasn't installed on the assembly line.
I will say that this particular car and the other I mentioned (it is also blue, but a lighter shade) were NOT invited back to MCACN this past year for the "W-31 Invitational".