A warning: in theory, the line to/from the booster is a dead end (no leaks) and should be able to run without regard to size. A large booster means (probably) a large volume inside the diaphragm, so that several stops can be made without "refreshing" the diaphragm from the manifold. When vacuum is exhausted, the pedal is hard until vacuum rises again.
The problem: if you run a large hose from the manifold, once the booster is at high vacuum the engine will not know it's there and the car will stop normally.
However, after a few stops in traffic, the diaphragm will try to re-charge from the manifold, and if you're idling the engine will see this as a huge vacuum leak - and stall.
I don't know the "correct" hose size (actually, the minimum fitting ID in the line), but I'd duplicate the original size if you can find it.
If not, I'd run a big line, but leave some fitting where you can reach it and insert a smaller fitting or restrictor if it stalls.
Why not just use a small line?
Because it takes a long time to fully re-charge a big diaphragm, and the engine will stagger for longer in seconds.
Best (although complex and annoying): use a solenoid valve in the line (hot with the key), which closes when the throttle linkage is fully relaxed - when you let off the gas, the valve closes. This will prevent any vacuum demand by the booster from reaching the manifold unless you're actually driving (when it won't matter).
