help identify - air cleaner base

[BACKN 68]

Could use some help in identifying a GM chrome open element air cleaner. The lid is the standard chrome piece, but the base is different from any I have seen. The base has 3 holes stamped into it. Two of the holes have a "rubber plug" inserted, and the breather tube is inserted into the remaining hole. What seems odd, is that the breather tube is not welded in, it is removable. I can move the breather tube from one hole to the next, by removing the plugs. It is a tight fit in the hole, but it is removable. The tube does not look like it was ever welded in. The seller stated the original application was from a '68 Camaro 396/375hp. Does this sound familiar ?

Thanks for your time,
Kent