Just picked up a older 700 and the Sear is 2 piece. Any reason for this when all the newer ones are one piece. Thanks

These were the "recall" triggers on 721, 722, 600 and early 700 model rifles. I, personally, have never had a problem with these triggers but with the great retro triggers available these days why take the chance on an AD?

Only thing I like about it is the safety locks the bolt in place. If I were to replace the trigger itself and use the original safety would that particular feature still work that way?

You can interchange those parts. I have triggers and the older levers.