Marlin Ballards came both ways, depending on the intended caliber.  I would guess that a .38 long, which is really a "pistol class" round, would come with a cast action.  You can tell by dropping the block out of the action and looking under the barrel.  If there is a rather significant void there, it is a cast action, while the forged actions are pretty much solid there.  The .38 you mention could go either way, but if it were a .38-55, it would be forged.

Froggie