EIDELWEISS,
The .45-120 is plenty for leopard and likely plenty for lion as well.
Heck, the .45-70 will probably get the same respect from people who have shot and seen shot quite a few large cats (I have not done so).
Many PHs will not guide for baited leopard unless the client is using a scope on their rifle.
Perhaps there might be one somewhere that would agree to your idea (it'd be a shame to have to scope a good looking hammer gun like yours).
Perhaps one of the PHs who offer hunting leopard with hounds would agree to your idea.
I do not hunt leopard because I am severely ADHD and cannot sit still in a blind very long ("ants in my pants") and am too old to keep up with a pack of hounds these days (youth is wasted on the young).
I can still walk all day with a large bore rifle and I shoot them very well but, I will never hunt lion due to the price.
However, if you do not find an Outfitter or PH here in this forum (there are several excellent ones here) that will accommodate you, I know one that occasionally gets a lion permit for a 100,000 acre concession bordering The Kruger Park, no fence between them, only a shallow river (I shot a 42" buffalo there, shown as my Avatar).
When he has a permit, he offers a tracking hunt on foot for true free-range lion.
You would be limiting your shot opportunity (wild lions are quite skittish/elusive/difficult to sneak up on) with no scope but, perhaps he might agree to your idea, I'm not sure.
Fly in the oatmeal - Those free-range lion hunts cost more than most folks can afford.
Best Regards,
Velo Dog.