most common cause of my silvia not starting was plugs covered in coke
take the dizzy cap off and examine the contacts; if they are dirty buff them clean with fine emerycloth/fine abrasive paper, if they're mangled [unlikely]then replace. test this by checking for conductivity from dizzy kingpin lead across to htlead pins while turning engine by hand.
if you have a multimeter put it on 20v range and over primary windings of coil see if you get 12v; otherwise maybe a spare bulb likea fog light?