Chrome: If it has the original finish, then it's nickel, not chrome.
S/N 505xx: This appears to be an assembly number (usually found inside the yoke, among other locations). The S/N is on the bottom of the grip frame.
Field Holster: Milt Sparks #200AW
'Beefed-up' N-Frame: If you mean a 'new' Model 58 like
this one, then no worries: Your gun should fit the vast majority of holsters made for N-frame S&Ws with 4-inch barrels. (Most likely all of them, but you never know...) Same for older M58s, too, since the so-called 'endurance package' is largely comprised of essentially
internal changes to the frame/design.
HTH
