check the valvetrain timing?
i forget if these are chair or belt
i think it has a chain
check valve lash and i forget how the ign times itself but check all the sensors (on the pre emission hysters with coil pack GMs)

does this have the emission system?
if it does make sure you have the trigger wheel (for the rpm sensor) bolted correctly to the crank pulley it only has
3 bolts so you have a 1 in 3 shot of getting it right
at 120 deg out either way youll never get it to work right
i had a hyster GM in my shop the guy took the engine out for a reseal then put this wheel back in the wrong position
and it had very similar results like youre describing
but if no1 took the engine apart recently this may not be the problem