Glad to hear someone's got the parts to send you.
Here's an older thread where I posted some pics and brief info about installing a sideplate without tweaking or damaging the plate's prongs, or legs. It's post #37 in the thread.
New acquisition-5906 (I broke it already)
I think I probably mention it in the linked thread, but the usual cause of a tweaked or broken leg on a sideplate is improper installation of a grip.
It's not uncommon for the front end of a sideplate to lift a bare amount from the outside of a frame, nor is it unusual for the end of the lever's plunger to engage the angled part of the sideplate at the bottom (when it's down in the normal position, with the slide forward).
I was so tired when I posted my previous thoughts that I forgot to mention another possible cause of your tweaked (outward) slide stop lever, which is that in addition to someone maybe having tried to force the front of the lever assembly by beating on the right end of the pin, they may have also tried to pry the rear half of the lever (like with a padded/taped screwdriver, etc) away from the frame, to remove it. (I'd just gotten in from a pleasant night at my cigar club, which had ended at midnight, and the drive home over the hill, after an afternoon with my granddaughter, had come close to wiping me out.
Trying to organize my thoughts in writing at 0200hrs isn't a common occurrence for me anymore, now that I've been retired several years. )
Hope the new parts restore normal function to your 4506. It's a beast of a .45 pistol.
Just for reference, if you use the factory recoil spring (and there's no reason not to, as they're good), this image offers some guidance from S&W in checking the free length. Remember that S&W offered both a standard spring (combat loads) and a light wadcutter spring (competition bunny fart loads).
If you use an aftermarket spring, though, it might be different. Their wire gauge, heat treat, number of coil windings and normal length might not be the same as the spring the factory uses, so the free length might not be comparable to try and estimate when a spring is "too short" or has become weakened. What you DON'T want to do is get an aftermarket spring that wasn't specifically designed for the 4506,and risk getting one that's too long. Like with a 1911, if you try to use a spring that's too long, it can stack solid before the slide has reached its rearward travel and the slide's dustcover can become damaged (cracked/broken).
Let us know how the "new" parts work. Luck.