Is there any hard data or information regarding the use of the 2 piece intermediate steering shaft on the later year Big Block Beaumonts? It is my understanding that the 69 Chevelle and later big block cars utilized a 2 piece unit, that was separable at the lower end by the steering box to aide in the removal of the steering column, due to the tight fit along side the big block exhaust manifold. 68s may or may not fit into this situation, but it seems pretty clear that the 69 model year was standardized on the Big Block cars. 

Here is a picture of the splined lower 396 coupling on my 68.