In this case, the Julian date indicates a 1970 build for the 1971 model year. For those of you who don't know, there was a strike at GM just before the car was built; they were out of BB TH400s but had some OW ones available when production restarted, thus what's usually an Olds transmission in a Buick.
I'll let Stefano comment on the car when he's ready, but it's not a small block (or at least wasn't originally if the VIN on the trans matches).
