722/700

Are they one in the same?

Can a guy use a bolt out of a 700 in a 722?

Are the stocks interchangable without major fitting?

The 721 and 722 where the predecessors of the 700. I doubt that any parts or the stocks are interchangable.

I have never tried it, but I have seen model 700 bolts used in 721's and 722's. BUT, you MUST check the headspace before using.
As far as the stocks go, it is not hard to fit a 721 or a 722 to a 700 stock. Behind the notch for the bolt handle, you must cut the corner of the wood for the safe to clear.
On 721's and 722's that have drive in rear sights, you must cut out the barrel channel to clear the barrel swell for the rear sight.
The bolt handle notch also has to be cut out slightly on the front side because the bolt on a 721 and 722 is straight down.
When using a 700 stock, it is a lot easier if you use a 700 magazine box and spring if it is a ADL stock and if it is a BDL stock use the magazine, spring, and dropping floorplate.
I once got two Bell and Carlson stocks. Both were 700 stocks. It took less time to fit the 721 than it did to fit the 700. They were both ADL stocks and I used a 700 box magazine and spring for the 721. If I remember right, I think I used the 700 stock mounting screws too.
I have also mounted a 721 in a 700 ADL walnut stock. Same way.

I think the SA 700 bolt will go into the 722, but not the other way around. The 722 bolt lacks the guide rib cut in the RH? lug. Either way, as with any bolt swap, headspace would need to be set and bolt timing/sear engagement checked. I'd check my LA 700 in the 721, but they are both buried in the safe at the moment.

The barrel shank threads are supposed to be the same.