After revisiting Dig's text, I now see that Westley Richards began with a toplever design in 1858, followed by improvements in 1862, 1864 & 1871, with the 1871 being the pinnacle I assume. So which design 1858, 1862 or 1864( No. 2623 of 22nd October 1864) had the 2 screws in the toplever like the GR in question? British patent #2506 of (10-9-1862)1862 possibly?

Here's a toplever thread: http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=58767&page=1

Kind Regards,

Raimey
rse