Places where a stiff clutch pedal might come from (or be contributory): Pedal assy., clutch cable, clutch pivot in bell housing, clutch cover.
The Rule of the Clutch: If you see the clutch, replace the clutch.
When you pull the engine and tranny, check all those areas. Given that you're pulling the engine and tranny, it sounds like you're not dealing with a reliable driver but more likely a rescue from extended inaction in which case, I would probably count on changing the cable anyway.