As far as rechambering and using the same barrel - 308, 30-06 and 300 Win Mag are your choices.
If you are wanting the change barrels....
Any of the 30-06 cases will work so 270, 280, 338 -06, 35 Wheelan, and 9.3X62
Any of the 308 cases will work so 243, 260, 7-08, 338 Fed, 358 Win
Any of the Mauser cases will work 7mm, 8mm, 7.65 and 6.5X55 (although the rim is slightly larger than the earlier cases mentioned). And odd things like 7.7 Japanese too will work if you have a large stash of .311 bullets.
If you are willing to change the bolt face.
Any of the belted short mags are possible - 257 Wby, 264 Win, 7mm Rem, 300 Win, 338 Win mag.
Any of the Rigy cased short mags too are possible 300 WSM, ect. Ruger short mags (375 adn 416) and some of the lazzeroni rounds.
Simply changing out the barrel to the caliber you want and have it chambered is all.
As for a safety there are two schools.
A is add a Remington 700 style and either keep the lever safety or replace the cocking peice with a blank one
the second is add a wing safety like a Win 70 or the new Ruger M77 MKII's.
These are simple to change out and it should only take a few minutes. Brownells has them in their catalog for under $200 in the white so you can have the finish match the rifle.