I have used a Maillard (Sachs) 6-speed block on two different 5-speed hubs (both Campag) and as the Maillard 6 blocks were about the same width as a Regina 5-speed, both would fit a 120mm rear dropout spacing. Using a 7-speed Maillard hub on a 5-speed hub would require a longer spindle and quick release and packing washers, and a 126mm rear dropout spacing (or cold setting a 120mm frame). If using an existing 5-speed wheel, the wheel will need re-dishing.