There were two different Field actions. One was a pure falling block and the other was a modified Martini (see https://www.tapatalk.com/groups/britishmilitariaforums/1877-field-s-rifle-t26802.html)

Both actions had side levers similar to the Hepburn or 1881 Deeley Edge. Both actions are fairly rare.

Don, Please post some pictures of your rifle.