I think that's a W.C. Scott. With the addition to the loaded window it became their "triplex action" that they made for a number of gunmakers including H&H. Here is my Reilly side lever with its twin, former Terry Buffum's gun, which is up in Massachusetts someplace.

[Linked Image from jpgbox.com]

Better picture of the Scott Triple grip action:

[Linked Image from i.imgur.com]

Reilly with the Scott action without the window:

[Linked Image from i.imgur.com]