pump-ready Classic Body?

[flampaint]

so I was taking apart my old Classic Mag with its direct feed body (ca. 1994ish) and I noticed that the bottom slot which is usually quite narrow (just wide enough for the sear to tip/rock back and forth) is a lot wider on this body and it has a groove which could be (I assume from the looks of it) for the pump rod...

Is my assumption correct and could this body therefore be used on a (rainman) pump-kit-equippped mag?
If not, can anyone tell me what this is for and/or what the added groove is for?

Thanks!