Marlin lever actions

[Larryjk]

Rustywreck, I don't know the answer to your question on the large loop levers interchangeability. As for the short tube on the long barrel and long tube on short barrel. I believe it is simply an attempt at gun balance. I used to shoot a Winchester Model 86 that had a long barrel and tube. When you filled the tube, you had an unusually nose heavy rifle. It sure did keep the barrel down when you pulled the trigger.
The longer tube on the short barrel Marlin gives you more weight out front which you need. The long barrel and a short tube keep from feeling like there is an anchor attached to the end of that long barrel.