Hi Alex;
The later 140GL's had the tandem 164 booster on them from the factory. Your 72 probably has the single booster (flatter in profile) compared to the tandem one. The later masters are identifiable as they have a steel sleeve hanging out the back and are the same part number for 164 and 140. The earlier 140 style master is quite different.
The large tandem booster does give a lighter pedal as they have more assist. I would not advise changing the hydraulics to achieve the lighter pedal effort - the bore is already quite small on a Volvo as with four wheel discs, they don't require much fluid displacement. It is the assist that should be changed.
In Canada (perhaps elsewhere) 240 carb cars came with a single booster, and fuel injection cars with a tandem. I have converted several customer cars to the tandem to achieve the lighter pedal effort.
There may also be a clearance problem with the right hand drive cars with the big booster....
Rhys