The diff is the safety and the bolt stop; the 722 safety is not let in the receiver, the handle part bows around the receiver, so a 700 stock needs modding. Same with the bolt stop, the 722 uses a tiny spring and a different looking bolt stop, a royal PITA to work on, but a 700 bolt stop won't work on a 722 because the the little notch for the bent piano wire spring ain't there.
I have a 722 based 40X and I was stumped by the how the bolt stop worked (didn't care about the safety wasn't gonna use it anyway), so I called Remington custom shop and left a message. Keith called me back and said he didn't know either but there was an old retired Remington guy working there on contract and he'd ask him about it. The next day he called me back and said yeah, but couldn't help with parts, etc. Keith asked how attached was I to the old style receiver because he had a proposition for me, he said send it in and he would have it machined for the new style safety and bolt stop and consider it a warranty job no charge. So I sent it in, with a real bad beat-up factory trigger attached; a couple weeks later Keith calls and asks if I want F and S engraved before he sends it to the bluing shop? I said sure, why not and he asks if I want a modern trigger installed, and I asked him how much and he said same price as he quoted me before, zero. Have you ever heard of a story like this about good customer service? I love 40X and this is just another reason why.
Thanks, Douglas