Master and slave are the same on all models. A new clutch will tend to need more pedal pressure, but this will reduce as the clutch wears. The larger clutch will require more pressure, but should not be that much more.
There are a couple of things you could check, but I do not expect they are contributing to the heavy clutch. One is to ensure that the pushrod length adjustment is correct for the slave cylinder - if this is wrong it will change the leverage a little, the other is to ensure the pedal pivot is well lubricated.
I seem to remember that some Defenders have a clutch assist spring, and since the pedal assembly is the same, it ought to be possible to fit this to the Series clutch.
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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