I've just bought a 1974 3500S Evoura and the brake pedal feels very hard. I've had the brakes checked and everything appears good including discs, pads and brake lines. Is this how the brakes should be or could it be a servo issue?
It sounds like a servo issue. With the engine off pump the pedal a few times to exhaust the servo, then hold your foot down on the brake and start the engine. The pedal should drop a little to show that the servo is working. If it doesn't, check that the servo hose isn't collapsed or blocked, if that's OK then it's the servo faulty.
Compared to a modern the brake will appear firmer. The V8 does not produce a huge amount of vacuum which is a factor as well.
You could always take off the vacuum hose to the servo, plug it and go for a drive to see what unassisted feels like.