Photos are of the RB distributor in a B block. This particular B block is a 400 but 400 and 383 are B blocks and share the same dimension for lower distributor shaft length.

1972 Pro-Street 'Cuda, 500" Eagle stoker B Block, Eddy RPM heads, Victor Manifold, 850 Mighty Demon, Hemi 4 Speed, Dana 60 w/4.88 gears - Built by Hansen Racing Middlesex - NJ