You must call S&W for a correct answer.
You should call S&W to get the correct answer from them.
The markings.
500$
yes
Best left to a trained gunsmith
I would start my search at Smith and Wesson first.
50- 325 USD or so
100-300 usd
Not recommended
100-3000 depending on specifics
You will have to find someone who specializes in air gun repair.
100-300 USD I'm interested in buying your 20ga S&W. Please shoot me an email at 71Rcode at verizon . net. Thanks!