The LD340 is absolute junk and you need to box it up and send it to me so I can properly dispose of it.
According to everyone I've spoken with, from Barton, to Ede techs that know the LD from years gone by, to my own experience... If you have an LD 340, save your money and don't buy an Air Gap. The difference in performance is about zilch. Sometimes old tech is just about as good as new tech.
Don't touch the Performer unless it's the RPM one. You're better off with a cast iron 70 340 intake than a standard performer.
If you still want to switch out manifolds, please let me know. I'm looking for an LD340 for a Duster 340 car.
Thanks