Re: 7rem mag to 300 ultra
I'm going to go out on a limb and guess a little bit.
The bottom metal should be fine. Think you'll need to replace the magazine box and follower. I think the shoulder on the ultra will be too big to feed well, you'll either need an ultramag box and follower or you'll need to convert to a single stack. (Uck.)
Best way I know to do all this is call the remington parts number and order what you want.
A friend o' mine has converted a couple rifles. He buys 700 ADLs cheap and converts 'em to whatever. I'm not sure how the magazine stuff will work out 'cause he's into this single shot stuff, target guns rather than hunting guns.
Flex is for people who don't have lockers.