Can anyone tell me if a Rem 721 will fit in a 700 stock?
Thank you.

Yes, that will work. A few months ago I put a synthetic stock on a 721 in.270. After looking for and not finding a stock for a 721 I was told that 700 stock is very close. It worked out very well. All you have to do is relieve the barrel channel where the barrel swells for the factory sight dovetail and possibly ( I can't remember right now ) a little around the tang

You will need new bottom metal, and a new magazine box. If you use an ADL stock, you'll only need a new trigger guard. When I switched to a 700 short action stock on my 722, I found that the old magazine box was too long. The spring and follower works fine, though. You will have to relieve the stock around the safety, tang, and the aforementioned barrel boss. It's the work of an evening in the shop or in front of the TV. (Although my wife did question the little plastic shavings on the couch, so you may want to watch that.) Changing to a more modern stock design certainly makes the old Remingtons more shootable.

Thanks guys. It would be an ADL stock. I'd like to lighten it up a bit....it seems very heavy.

Maybe it makes a difference who makes the stock that you buy. I used a Butler Creek stock and the orignal trigger guard and magazine box worked just fine. There were no parts that had to be replaced