"Why the JC FN Mauser over the Dumoulin Mauser?"
Simple because they're the same as the Browning FN Mausers. The Brownings has some slight modifications that really don't do much but price wise, the Sears M50-M51s are a good action and comparable to the Pre64 M70s which they competed against. Check out some of the older gun digests from the mid 1950's and you'll see the prices for either were very close. Frankly, I prefer the Higgins FN over the pre64 M70 and I have owned both. The M70s are long gone.
You can find a clean M50 for about $350-$500 depending on condition and they come in .270 Win. and 30-06. The stock is a bit clubby but clean up nicely. Barrel are usually in great shape as they're chrome lined. Most shoot so well I haven't converted them to something else yet. Something about not shooting the donor. About the only change I have done to any of mine is replace the trigger with a Timney and frankly, that may not have been necessary.
Probably the best way to answer your question is to locate one and check it out for yourself.
Paul B.