[bonjour]

Any idea of the yeast viablility on the 1946 brewings?

At the moment, no.
However  the next bottle I open for evaluation will be one from was was (as far as I know) the last bottling (brewed '46 with the yearly top-ups, until bottling in '66) and I am going to be careful with handling, so I can try and see if it's possible to get some yeast going from the dregs. 
The yeast they used for the ferment was, of course, BRY96 (aka 1056, 001) though it would be interesting to see what characteristics are to be had from something cultured up from 43 year old bottle dregs !  Given the nature of these remnants, I will  enlist the help of a biologist friend who has offered to help out...she has indicated that using various media for multiple cultures may increase the chances of retrieving something. 

As they used to say on TV, "film at eleven"     

When you do these 'rare' beer tastings, please post them in a 'Rare Beer' thread that you start.

Thanks

loooking forward to your review.

Fred