The pre-c Leicas had a body that was built-up from stamped sheet brass.
The -c and later Barnacks used a die-cast body housing that was more rigid, and probably less labor-intensive to build.
I have seen many comments over the years about some folks preferring the "smaller" pre-c Barnacks...
I cannot say that the size difference matters to me one way or the other, as whatever Barnack I'm shooting rides in the bottom-half of a III-g case with a wide "hippie-strap", and I keep an accessory finder in the shoe. It's not a streamlined rig, no matter which series of body.
The older Barnacks are a loose fit in the case, but the case-screw keeps them in place.
For what that's worth.