I have used the S+K but not the B Square. I would say the S=K is OK its very beefy, and once locktighted in it never moved. I was able to look down the irons if they were cranked all the way down, which worked well for close in stuff in the scenarios at sniper school.
The Key to accuracy on the M14 is keeping everything as smooth running as possible. Make sure the oprod is running true in the guide, with no resistance.
Make sure the gas piston is moving smooth in the cylinder, easy way is to remove the oprod and tip the rifle forward and back, the piston should move freely. Same on the oprod, with the spring out it should move in its travel very easy by tipping the rifle forward and back. Check the gas cylinder make sure it is a NM pinned assembly to fully float the barrel. Last and most important the stock must be a very tight fit. The resistance on the trigger group when you close it, should start at about 2/3 way closed, and take some effort to close fully. Most wood stocks will require glass bedding to get the best fit. For a bipod, use a glassed or epoxied in QD stud in the forend, the military ones put up pressure on the barrel.
Checking all these items and using a standard M14 USGI rifle with a WIN receiver, and barrel, and mixmaster parts, I can get MOA with 168 GMM rounds. I may mount a new NM grade barrel on this rifle and see if I can get sub MOA after truing the bolt and the new barrel. Mine is mounted in a USGI fiberglass stock.
MOA should be no problem with that rifle the barrels are better by far than USGI. One quick thing I forgot, make sure to store it wth the trigger group open. If it is stored closed, the stock compresses, the only thing holding the M14 stock on is the trigger group compression, so on a wood stock leave it open for storage. This is also true for garands and is how all mine are stored. One last item, make sure you use lubriplate or similar grease on the wear areas, the 14 and garand were designed for grease lubrication instead of oil. Let me know how she shoots, and enjoy her they are fun.