I'm all for customizing and having options, but be aware that any of the parts you replace are just as likely to need fitting as they are to be drop-in. You can't just replace the hammer, sear, slide stop and thumb safety and expect the gun to function exactly like it did before. Make sure to keep the factory parts if replace anything because in the long run those parts are probably the best option.

If it makes you feel any better some Colt's come with a plastic mainspring housing.