Drop ins
While the Wilson "drop in" beavertail may work (functionally) on your SA, be advised the tangs are cut at a different angle and radius and it will not "fit" as well as it would on the Colt it was designed for. Smith and Alexander makes a beavertail (Not drop in) specifically to address this. Now that I think about it, Kings Gun works makes several styles of drop in BT that might do it for ya. Never tried them in a SA.
I know of no aftermarket extended safety which is drop in, You might get away with a Para factory one, if you can live with the style, or a Colt if you can find one ($$$), maybe a Kimber factory from ebay? They will be fitted to work with a production gun already and will probably "work". Though have found it not too difficult to fit one. Kuhnhausen manual is helpful, but its' a bit tricky.
Chip McCormick hammer will "drop in", or there are several "Triggerjob in a package" options available (Cylinder & Slide comes to mind; see Brownells; Their catalogue is a great one stop resource for finding "whats' out there"; you really must get one!).
I used to like to use the McCormick drop in hammer (may as well get the sear too) and replace the GM grip safety with a "pigtail" Commander safety as an interim until I could get a gunsmith to install a BT.
Cheers, TF