Here is a brake that is on off. Don't know any thing about it other than when I was researching brakes I bookmarked it. The advantage is you do not have to unscrew and remove it and then put it back on. Therefore it should not be shooting loose.
You might consider Big Bores advice and think about a Plan B
Get a quote on what you want from a gunsmith if you supply the action.
Visit every pawn shop within 50 -100 miles looking for a great deal on a really beat up looking Rem 700 or a Savage ??? that appears too have a good action. Buy it for the action and throw the rest away. Send that off to a gunsmith. I don't know if it would really save much money. But it will certainly kill some time visiting all of the pawn shops.
If you are getting a barrel then you can pretty much choose any caliber that fits your action.
The 30-378 will burn a dump truck load of powder. You don't even have to put bullets in it because the muzzle blast alone will kill every thing within several miles.
Depending on your definition of long range and your opinion on terminal energy the 7mm Rem Wby RUM or STW are capable to 1000 yds or more. The 270Wby, 264 Win about 800yds. These can be stretched further with high BC bullets.