I agree with Dr Bob;
To the best of my knowledge Lefever first used a top lever in the late 1880's on the "Automatic" Hammerless rod cocking gun. This lever was a side pivot one. The gun pictured shows a central pivot lever which Lefever did not use until about 1890 on the Two Hook hammerless guns. Have never heard of a Lefever hammer gun with top lever opening. The thumb push continued through the Side Cockers with internal hammers & on into the early Rod cocking hammerless as mentioned.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra