If you don’t have any real emotional attachment to the rifle and it is an m70 XTR, you might want to consider selling it if it doesn’t run afoul of your family. find the model number and look around online to get a rough idea what it would sell for. I think the XTR was a push feed rifle and not like the pre-64 or classic rifles with controlled round feed so nothing special for collector value. You can get a gunsmith to put a new barrel on it and true up the action a bit but it isn’t the most cost effective option.Savage, Remington, Ruger, and Tikka all have designs that you can rebarrel yourself with a barrel nut in any chambering you’d like without any machining. I will say that modifying a hunting rifle into something for a match style rifle is often really expensive you’ll have somewhere around $1000 for a match style stock or chassis (if you can find it), probably around $1000-1500 to rebarrel true the action and tune the trigger, and then you’ll still need a scope ($700-1500) and mount($100-400). After all that you still have a mediocre push feed action with a 90 degree bolt throw that won’t fit any popular chassis system . If you sell your rifle, you can apply that cash to buying something that is already close to what you’re looking for, and will be easy to modify to your liking later. A Remington 700, Ruger rpr, tikka T3, or even a dirty savage model 10 will be available for anywhere between $350 and $1500 depending on the model and sales and then all you would need is a scope and rings, you will spend the same amount or more to make a model 70 into a long range precision rig, and you may have screwed up a pretty fine hunting rifle. Try this; Buy a box of 6.5 and a box of 300 win mag, ask your buddy if you can shoot his rifle to compare the two, shoot 4x 5 shot group with your buddies rifle first ( that parts important) then shoot 4x 5 shot groups with yours and compare the group size. Then you can decide if you really want to drop $2500 into a $500 rifle that hurts to shoot. Any of those rifle platforms mentioned will get you plenty of accessorizing potential and a pretty accurate starting point, and they’re all offered new in the tacticool black or tan outfits that everyone likes so much these days. You could always keep the m70 for hunting and buy another rifle, there aren’t any limits on how many you can own (if there are, they aren’t constitutional).
If you go that route and end up buying a new rifle, ask yourself a few questions before you pick a cartridge. How long is the longest range available in your area? Do you have any interest in reloading ammunition? Do you have any thoughts that you might like to hunt with it? 300 win mag is a great round and it is very versatile for long range target shooting Out to a mile or more and hunting anything in North America but if you live in the southeast and only have access to 300-500 yard shots, that level of overkill gets really expensive and painful to shoot enough to get in good developmental practice, while A .308 , 6.5 creedmoor, or even a .223 give you a lot of cheap practice with factory Ammo and you won’t have a flinch after shooting 50-100 rounds on a Saturday. A 6.5 is hard to beat for new shooters, the recoil is pretty mild and there isn’t much the round can’t do. .223 certainly has an edge for cost and low recoil but downrange energy suffers for hunting and that low recoil can cause problems down the road if you develop bad habits for recoil management.