Question about the magazine tube on a older M1 Super 90

[JeepsAndGuns]

So I am looking at a couple older HK marked M1 Super 90's for sale. I am trying to find out about the magazine tubes on them. 

One has the full length mag tube that is almost the same length as the barrel, and the other has a shorter mag tube that extends only a couple inches past the fore grip. 

I have a older HK marked M3 Super 90, and the full length mag tube on it, is all one piece. 

What I am wanting to know, is are the M1's the same way? Is the mag tube one piece, or is it two piece like most other shotguns out there? 

I tried to search online but did not find a answer, however I did see mag tube extensions labeled for the M1, so that would make me think they are two piece? 

Reason I ask, is my M3 is HK marked, has the pistol grip stock, ghost ring sights, and full length mag tube, and I want a M1 in the exact same configuration. 

The M1 I found with the full length mag tube, has the standard/rifle style stock and cylinder bore barrel, while the one with the shorter mag tube has the pistol grip stock, but also has the barrel with screw in chokes (which I really like and want). 

So I was just curious if the mag tube is two piece making for a easy swap to a full length mag tube on the one that currently has the short tube.

[JeepsAndGuns]

I ended up just buying the M1 with the short mag tube. I was not having any luck finding the pistol grip stock in stock anywhere. Plus it had the screw in choke barrel. I could find mag extensions pretty easy.

The mag tube is two piece like most other shotguns. It ends at the front of the foregrip and it is held on by the mag tube extension/nut. 

Figured I would update just in case someone else stumbles across this and wonders the same.