The bb1600 has a more “shouldered” feeling neck, it’s a tiny bit chunkier - but not in an unpleasant way. Very much like the 1985 bb1100 I had. The 414 is slimmer and shallower like a flattened C shape - they reverted to the deeper feel on the 424…
the body shapes are pretty much identical - slight variation on the treble cutout - about 5mm deeper on the older 80’s BB’s.
The bb300 when I was a kid was a mega early Japanese one with the really shallow treble horn cut out.
I don’t get involved in measuring necks/string spacing etc - I either get into a bass or I don’t, I never buy something just because of string spacing/nut etc.
😉