The SMAV-3 is a 3-way that can be plumbed normally open or normally closed. An MSV or MSV-2 is a 3-way that can only be plumbed normally closed - but is also not cylindrical and is quite a bit larger than an SMAV-3.
You can use a cocker ram with a 3-way, just hook a constant air supply to the side with that the rod comes out of and cycle the air only on the back side. No need to find a spring return ram. Just uses the different surface areas on each side of the piston to control the movement. You will have a lower force extending the ram than if you were using a 4-way, but the retract force would be the same as normal.