I recently bought a 1981 F-100 with a 300 inline six cylinder. The truck willl turn over but not start. I have checked the timing and it is okay. I have replaced the Duraspark module, ignition switch, distributor pickup coil, ignition coil, plugs, wires, cap and rotor. It has spark but will not start. It is getting fuel. It tries to start but wont. The only unusual thing that I have found is that it will crank in any gear. I thought if the neutral safety switch is bad it will not crank at all. I can't seem to find the problem. Help!

Thanks in advance!