Cletus - The original part number is GM# 3835776, and they are 10-7/16" long. There are a few "used" 216 push rods in various ads on evilbay (both individually and as sets of 12), but honestly I'd vote for spending equal or lesser money for some new replacements from either of these vendors:
The Filling Station
AF-449 @ $7.70 each plus shipping
OR
Chev's of the 40's
PN 3835776 @ $7.75 each plus shipping.
Some other vendors offer them new as well, but at substantially higher prices, like $15-$20 each. Ouch!
There is probably a fellow 'Bolter that has some stashed away, but if no one offers them up, you have these options.

Best of luck on your hunt!
