Just 2 side notes:
1) I'm not sure there ever was a no kidding "2Bore" hunting gun that was actually that. It has been written about "2Bore" shells (ie: 1/2lb) being used however those possibly fired out of something not of actual 2Bore internal barrel diameter.
That said, there are one or more modern made actual "2Bores" kicking around and I think YouTube videos of such.

2) 85lc….a proper weight 4Bore is not THAT much more enjoyment (punishment?) than a 10Dram 8Bore. the worst part is the notion of carrying the thing. Of course back in the day that is what gun bearers were for……
Many years ago I got to fire Ray Meyer's 4Bore Thomas Bland single shot (a fella in Montana has it now) with proper black powder and conical ball loads, after 2 rounds I'd had enough. Of course that was after already having fired 6 shots from my 8Bore….. no headache and only a bit of a tender shoulder.
At my present age I'm not inclined to do THAT again.

As they say: "Go big or go home"

- Mike