FW...you notice I said..."CHECK THE HEADSPACE"..."..."BOTH CASES ARE SAAMI SPEC'ED TO THE SAME PRESSURE"...you can check that for yourself..."FOR ALL INTENTS AND PURPOSES, THE 307 AND THE 308 HAVE IDENTICAL CASE SPEC'S"...except one has a rim and the other is rimless.
I don't advocate ANYONE doing ANYTHING unless they thoroughly understand all the ramifications, I just responded to a question from the perspective of "been there, done that".
As I said I shot 356 W/358 Win (nothing but 307/308 cases expanded to 35 cal without any other mods) loaded ammo interchangeably and intermixed in my 356 Win, Marlin 336 levergun...and have use all the other listed cases with the required forming. This is not to say I have a magazine full of intermixed ammo in my 356...doing so causes a big ruckus with accuracy...just that it can be done with minimum problems as long as you follow good reloading practice and understand the inherent problems and do the require things to solve them...
I use one set of Lee dies marked 356/358 to load the rounds and do much of the forming.
I don't have an NEF 308 Survivor to test so I can't say for certain if I could be done or not...I didn't specify a gun maker other than my Marlin 336 in 356 cal...but I have shot 307 W cases loaded in three different sets of 308 dies...RCBS, REDDING AND LEE, in two different 308 cal bolt guns/barrels while I was working through the 356/358W process just to see...I didn't have ANY problems with using the 307/308 cases as long as the sizing die was adjusted to fit the chamber of the particular rifle/barrel I was shooting at the time. The rimmed and rimless cases fed, extracted and ejected without a hitch.
It may be as simple as just resizing or it may entail a more lengthy process...information on the "how to" aspect can be extracted online, in many reloading manuals or by experience...I've been doing this "reloading thing" for over a half century and the internet isn't a substitute for self education...I can't and won't try to reduce that level of experience to a few lines of print on a forum...if you don't quite understand or want to learn more, break out the books and start the long process.
I also continue to say..."don't ever use ANY data or information you find on the net unless you are a very experienced reloader and understand the whole process...reloading, case forming, SAMMI specs, headspace, chambering, receivers and pressure...to just name a few.
There are several good forums that have dealt with this same 307/308 - 356/358 conversion at length...Beartooth, Accurate Reloading, LeverGuns, etc...if you are interested, do a search on those sites for additional information.
The best way to insure consistent accuracy and ammo quality for break action guns is to adjust your sizing die so the action has a nice snug closure on the reloaded ammo...this insures minimum headspace and takes up any slop in the hinge pin. The best way to insure the cases stay within that narrow window is to keep the pressures down...I garontee none of my breakaction shooters respond well to high pressures and that includes NEF, T/C Contenders and Encores.
One case in point...a 22-243 Midd...Ive had both bolt guns and a rechambered Encore in that wildcat...while I can get higher velocities than the 22-250 in the Encore, and the rechamber was done to correct an over length throat, I can't get anywhere near the velocity in the Encore that I could get in a Ruger M77 without the action locking up. As long as I kept the pressure and velocity down around the 50 KCUP range in the Encore I still got higher velocity that with the OEM 22-250 and once the dies were adjusted correctly the accuracy and case longevity increased by a factor of 10.
Another case in point is to headspace on the shoulder for belted cases. Different brands of belted cases have different headspace. To ensure case longevity headspacing on the shoulder eliminates this problem...but how many bother with it...I use only once fired cases for hunting anything larger than a coyote, but try to extend the life of cases used for hunting varmints...but then again I only shoot a few rounds of larger caliber rounds a year while shooting 1,000's of rounds at varmints.
Again this points to the fact that many reloaders have no clue when it comes to "benchrest prepping" there ammo and many don't want one...Not a problem...each person has different requirements when it comes to his fact of shooting and each will work through the problems or not as their needs dictate.
This sport is as bad as golf...some enjoy just whacking the ball around and enjoying a day out...some get wrapped up in the nuances of all aspects of the game...and the rest fall somewhere on the line connecting the two extremes.
It's all fun and enjoyment no matter where you end up.
Luck on your projects.