Good comments, Dave. I get awfully tired of the "only the factory can do it right" crowd, and most Smiths are badly oversprung. As for variations in strain screws, I've seen a pretty wide variety, both in head thickness and screw length.
To change the firing pin: Pop the sideplate. You'll see the firing pin retaining pin protruding slightly, right in front of the hammer, where the very top of the sideplate fits. Take a punch and depress the firing pin a bit, to remove tension on the retainer pin. It should be pretty loose in the hole. You can either roll the gun onto the right side and let it fall out, or pluck it out with tweezers or small needlenose pliers. The firing pin and spring will now come out to the rear, with the hammer pulled back a bit or cocked. Reverse to install the new pin and spring.