M1 SP vs Air Gap

The LD340 is slightly shorter.

4-5/8 front by 5-9/16 at the rear.
Compare at http://edelbrock.com/ for specs of the RPM.

As listed by Edelbrock's site. Manifold height: A-4.75", B-5.8"

(Port size is .98" x 2.16". and the LD340 is a near perfect match for the Fel-Pro gasket. )