Looks great, Neil ! You are correct, those old Stevens rifles don't get enough credit, IMO.. Each one I have dealt with, has been a real shooter.
A couple years ago, i saw an old Stevens 66B "Buckhorn" .22 at a LGS. I bought it for $100, my top price for an old .22 rifle. It was probably about 70%, being generous.
Ejectors were not working..found the tiny springs all clogged with black crud..perhaps burned powder? It was missing rear peep/combination sight. I was told that if I fond one, it would cost as much as the rifle. Brousing through a gun show a couple months later, I spied what I thought may work, in a spare parts box. The lady said it would set me back $20...guess she felt sorry for a guy with such an ugly face..come to pay, she dropped to $15 !
Got the steel cleaned up, refinished the stock...and found I had snagged a top shooter! With irons, I could set up a clay pigeon at 50 yards..bust the pigeon..and then bust the pieces of the pigeon!
On your rifle...you are obviously correct on the worn bore, but it wouldn't hurt to try another, possibly helpful trick..check the barrel crown! I have an old Mossy .22, that doesn't shoot very well. Bore good, next move is to recrown the barrel. I can visualize some previous owner, running a cleaning rod through from the muzzle...and bouncing the cleaning rod, much like the movies show old timers bouncing their loading rods on the old muzzle loaders.