If I'm right, you're going to be kicking yourself...
Does the car has a clutch stop? If the last owner put in a clutch stop, you may not be able to push the clutch down far enough to click the clutch ignition lock interlock. When I bought my car, the PO put in a clutch stop that would sometimes require a couple of hard stomps on the clutch to get it to start. Instrument panel lights come on but no cranking when the key is turned. Replaced with with my own homemade clutch stop and it's worked flawlessly since.