184826,
As it turns out, my machine is one of the fairly rare 1947 intermediate bed models.
1947   SB9A.   4' bed,
intermediate casting.
"South Bend" cast into top of 2 bed ribs.
overall condition good unrestored.   Its definitely been used,
but the bed, castings, and all the important bearings/bushings are healthy. 
Current location, Seattle WA.
I bought it in 2012.   Prior to that it was in storage for some number
of years at a hobbyist/semi pro race car shop.
I dug about a gallon of sawdust out of it.   No other history known.