How can you restore lost factory installed apps. I can not download some of the apps as they say they will not operate on iOS below 4.3

I'm assuming that you mean apps that you've downloaded from the store, as opposed to those that are built-in to iOS. Only the current version of each app is available in the store, you can't download past versions of them, so unless you still have an older version of them somewhere (on your computer, on a backup) then you won't be able to use them on your iPhone.