Hey.
I know they say not to, but I say who cares.
I ran a single plane intake on a 355 in my 81' C10 pickup and still hauled 1000lbs in the bed with no problems in loss of torque...the rear end had real highway gears, but it is a manual tranny too...but not a granny gear tranny(3+1 overdrive).
I had no problems and really couldnt tell the difference between the performer that I took off in favor of the single-plane.
The single plane was a weiand IMCA low rise intake....similar to a torkerII.
I was very please with the performance....even in the heavy pickup truck.
So from now on...I'll never run a dual plane intake on anything other than a "truck or economy" motor...like a 305 or 265.
The trucks motor had a 3 angle valve job and 1.94/1.50 valves with a cam that boasts .447/.447" lift and 222/222 duration @ .50.
It pulled really hard...even from a rolling start and would fry the tires WITHOUT a clutch dump....this is all with a single pull rearend with 2.65:1 gears.
In my opinion...the perfect intake for the street (especially in a light car like an H-body) is a single plane or a well tuned tunnelram.
Given my motor had no Air Conditioning but did run a power steering pump.
I even managed at one time to knock down 21 MPG on the highway with the single plane and an edelbrock 600....with a complete engine and tranny in the bed (850lbs).
God bless
-Shred