The 916A does not have an interchangeable barrel- the owners manual indicates that barrels are not removeable, but are permanently installed at the factory. The link below will take you to the owner's manual for the S&W Eastfield 916A.
Yes, they made it.
Needs to be examined by a gunsmith.
Best left to a trained gunsmith.
If it is not choked to tight, yes.
NO sn data for this S&W
100-300 US Dollars.
100-225 USD or so
300 USD or so
Try gun shops, pawn shops, gun shows, e-gunparts.com
Unlikely
Contrary to the previous answer, S&W did make a 916A pump-action shotgun (as I'm sure the questioner knows), but it was swiftly withdrawn from production and most examples were recalled, as they were prone to barrel ruptures. A 916A 'Special' was produced, but it was nickel-plated, rather than stainless steel. Hope that helps.