I think the trick to make stock stroke motors run well with IDAs is to drill a 3rd progression hole. Stock stroke motors dont have the displacement or the torque to make a smooth transition from the idle circut to the main circut, my opinion.
And about airfilters, unless you are driving on dirt roads, leave them off!! In 2002 a good friend of mine and I drove his 2276 IDA '68 bug to the first Drag Day from Phoenix (about 400 miles). We got caught in a NASTY dust/sand storm on the interstate, couldnt see 20ft in front of the car! And his car is equipped with huge Berg velocity stacks and a popped decklid!! Anyway we drove through it, got to LA, raced the car, and drove home. A few months later the engine came apart for maintainence/upgrades, and you know what?? The pistons & cylinders were perfect! They were reused! Big motors will swallow it up and spit it right back out the exhaust