I think your tranny is messed up. When I first drove my Z with the T56 in it, I backed out onto the street, put the the lever into first, let the clutch out and it stalled. Every gear I tried, it would stall. Turned out reverse and I think 6th gear jammed together inside the tranny, but the lever moved freely in all gears. Did you try connecting the clutch peddle, then push in the clutch, and see if the motor turns?