Technical Corvair steering wheel spline count question?

From doing a search, the 64 - 66 Corvair steering wheel had a smaller diameter hole and spline count than bigger GM cars. What other GM cars had this smaller splined steering column shaft? Maybe Vega was mentioned here? Other than finding a steering shaft in the used parts world, could a splined shaft be purchased? Just need the upper splined shaft to make an adapter to use with a 3 bolt column.

 

Vega is the same as Camaro, Nova, Chevelle, Full size, Truck at the steering wheel end....pretty much everything from 1965-1990ish except that pesky '64-66 Corvair deal.
Vega lower end at the steering box connection is 5/8-36 spline, smaller than the more typical 3/4-36 on most everything else.

 

Clark's Corvair Parts in Mass. may have column for that wheel.

Phil