Hi Adrian. My bike has a Shimano 7 speed internal hub with thumb shifter. As with yours, the axle is slightly wider than the 120mm rear width. I measured the opening with the hub installed and I've got 128mm. The width needed to accommodate the new 8 speed Shimano Nexus internal rear hub is 132mm. I'm concerned about the chainline and if the wider width required to install the hub would affect it.