Both great suggestions! Thanks!
Today, I pressed the Billingham Hadley Pro into service. The 503cxi and Leica X1 filled up only half the bag but I was surprised how well the Billingham fit my shooting style with the Blad around my neck.
It was quite ergonomic considering my fumbling around with loading 120 film.., LOL. All I need now are two more film backs (pre-loaded) and a lot more shooting to get my stride.