I've been through this process a couple of times, and my first word of caution is you need to get most 440s rebuilt and upgraded before swapping. I've known a lot of guys who thought taking a 440 and dropping it in was going to give them a high performance road rocket and were very disappointed when their car's performance was less than it was with the small block. Most of the lower-cost complete 440 engines I see for sale are mid-late 1970 motor home and truck engines, and performance wise these are pigs.
It's recommended to have any engine rebuilt before swapping it in since it sucks to have to pull it later on, but if you want better performance you're going to need a set of good heads, a better cam, an aftermarket intake, better carb, better fuel pump, torque converter (if you're going auto), and good headers. Then you'll likely need to upgrade the rear end gearing to get the right feel.
Finding and buying the engine is just the start of the process.