The second and third generation S&W are totally different except for the upper slide assembly. It is way beyond a few cosmetic differences. The trigger is vastly improved on the third generation units and many parts do not interchange. We have used both extensively since the mid 80's and they have been trouble free. The only problem on the second gen units were the ambi safety falling off. There is no way to keep the screw tight. We swapped out those for third gen safeties but they are tough to find today. While it can't hurt changing the springs, we have units still in operation since 84 using original magazines and springs. Zero problems. I would suggest getting someone who is a S&W armorer to swap out the springs outside of the mainspring, recoil and firing pin spring. Hate to see you wind up with a pile of gun parts.