I believe the split shaft was used to adapt a part GM made for a different engine so they did not need to make a correct-length part for the 250 and 292. There is no good reason to have a 2-piece shaft, as the distributor and oil pump are in a straight line with each other. When I rebuild that type of distributor to use on the earlier engine with a point type distributor, I make a correct-length shaft and eliminate the flex joint. I can see no good reason to have a flexible coupling there- - - -it's just another potential point of failure, one that would cause a loss of oil pressure and a locked-up engine.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!