This will answer at least one of your questions (from the FAQs section above):
Sources for choke tubes for H&R shotguns that use choke tubes?
MSP Ret
posted December 28, 2003 07:10 PM
The Winchoke system of chokes = Winchester/Mossberg 500 series/Browning Invector, will fit the H&R shotguns that accept choke tubes.
Also, I'm sure the finish is brushed nickel if it's factory. Other than various grades of blue, and camo on some specific guns, I've never seen another factory finish on an H&R/NEF.