The larger cabin Fish was called a Marlin, the last few hulls of the Fish design built by HMC. My sister has one, called Matsya. I think there were only four or so, built in the '30s, but the HMC records are clear on this. The cockpit is narrower than a Fish, the tiller comes over rather than through the transom, and the cabin trunk (still pointy at the forward end) runs well forward so the mast steps through the cabin top rather than through the foredeck. Some had auxiliary engines.
I believe all the boats called Fish or Warwick Neck Class originally had the short cabin. My boat (now Felicity, perhaps originally Felix, hull 972) was modified to be more like a Marlin by moving the aft cabin bulkhead aft two or three frames, making the cabin much larger, and putting on a sliding companionway hatch. I think that was done in the 1970's when she was owned by Peter Strock of Vineyard Haven.
There is another boat that I think is a Marlin here in Falmouth, albeit with a rectangular cabin trunk, which has been out of the water for decades.
Hull 1420 (1937) is listed as a Marlin.
By the way, my sister purchased her Marlin in Noank two or three years ago, so it may have featured in this discussion.
And the Cape Cod Shipbuilding version of the Fish is also called a Marlin. It has a counter stern (rudder inboard) and a very different rig.