Here is an original Hepburn rifle (not mine), guarded by two of my Ruger #1's. The lever that drops the block is quite visible.
There are a couple people making modern repros of the Hepburn. Here is DZ arms:
http://www.dzhepburn.com/gallery/A few other rare actions used a side lever to drop the block. This Rodda Field's Patent that I owned for a while is one example. Another one I should not have let get away