383 runs like a giant turd WTF

That combo,I would consider adding a good dual plane,and possible some Rhoades lifters.If setting the distributor curve doesn't work.Had a similar situation in a 396 chebby.Idle vac was 5 to 7".Curved the distributor,threw Rhoades lifters at it.Idle vacuum,(and low end torque!) went through the roof.Idle vac went to 12,and rock steady.That helps low end drivability,with a steady vacuum signal.