Yes, they are nice!
However, they are nickel plated, not stainless.
Don't have my Blue Book available to tell you exact years of production, but, about 1976 - 1986 would be a good guess
Here's a pic of my 1980 model.
One of my 9 H&R convertibles.
I believe H&R offered a total of 5 different 22/22 mag convertible models.
Model 649, 2 barel lengths
Model 650, 1 barrel length
Model 666, 1 barrel length
Model 676, 4 barrel lengths
Model 686, 5 barrel lengths
The model 666 is the only one that I don't have any examples of.