What master cylinder is this?

I'm working on restoring a set of Pentagram wheels for an XS650 project. They came off an XS500 and that bike seems to have been converted from drum to disc.
I have all the stuff to swap in a disc brake swing arm, but the more I look at this stuff, the more it appears I could use it with my drum brake swing arm with very little effort.

What master cylinder is this? Are rebuild kits available? What is the green thing/stuff that seems to have come loose inside the plunger mechanism? The only markings on it are "7/8", which I guess means it has a 7/8" bore.

If I can make this work, I think I will. Simply for the "weird" factor, if nothing else. Plus, I can keep the drum brake swing arm set up if I ever want to switch back.

Looks like an old Wilwood sprint car pushrod master.

I'm now thinking Hurst Airheart. If I can just figure out their parts numbering system so I can tell which rebuild kit I need....

I have the same setup and my master cylinder is a Hurst.
I don't have any idea what model. The m/c was sold as a kit with the wheels.

Rider

Yes, I had determined it was a Hurst Airheart and have a rebuild kit on the way.

What can you tell me about the kit? There's not a lot of information out there about these wheels or the kit.
I have a thread on the XS650 forum about restoring and fitting them. I'd love to know any history or info you could add.

http://www.xs650.com/forum/showthread.php?t=40530