Hi guys, need some help here. I'm looking at buying a 70 Cutlass that is believed to be a W31. The engine does not have the big balancer but does have the 7040255 carburetor. It does not have the original intake manifold. It is a factory 4sp car and has the 12bolt rear-end. Both the engine and the transmission are original to the car as they both have the partial matching vin. Was there any engine variations in the W31's such as the balancer?

 

No, the balancer is 1 of the man identifiers. The carburetor is also special. If you think the engine is original and if you can pull a sparkplug, look for flat top pistons. The distributor is the same as the 310 hp 350.

 

Every single A-body made by Oldsmobile in the 1970 model year came with a Type O rear axle that has a 12 bolt cover, but only ten bolts holding the 8.5" ring gear. This is NOT the Chevy "12 bolt" axle. Post a photo of the '255 carb number. It could be a restamp. Even if this car was a W31, the parts that make it so apparently are long gone. You would need to pull the heads to measure the valve sizes, and even then, it is easy to machine any SBO heads for the larger valves.

 

TLDR: Absent ironclad paperwork, there's really no way to authenticate a W-31, at least not with any certainty.