OK, the failure to eject sounds like your gas system isn't properly set up. Federal ammo is loaded very lightly when compared to surplus or imported commercial 8mm. If your gas system is set up for heavier loadings, then there probably isn't enough gas getting to the piston to reliably cycle the action.
To adjust the gas system, take off the top, front handguard. There is a spring-steel sleeve around the gas tube. Rotating this sleeve will move it back and forth either exposing or covering up a small hole in the top of the gas tube. For lighter loads, you want more of the tube covered (thusly bleeding off less gas) and for heavier loads, you want more exposed (thusly bleeding off more gas). The proper technique to adjust the gas system is as follows: expose the entire gas vent (the hole) and load two rounds into the magazine. Fire one round and if the action fails to cycle, turn the adjustment sleeve one click (covering more of the vent). Repeat this procedure until the action will cycle ejecting the spent round and feeding the next. Once you've got it running reliably with two rounds, load it with three and repeat the entire procedure. Keep doing this adding one round to the magazine until you can go through an entire mag reliably. Once you can load and fire all ten rounds reliably, replace the handguard and enjoy your rifle.
How badly is the stock broken? If it's just a small chunk of wood, your rifle is probably still shootable but if the action is now loose in the stock, you'll need to replace it. I doubt that the stock broke because of improper reassembly, it's not really all that complicated to remove and replace (at least my AL 30-06 isn't). More likely, the stock was weakened when it was modified (FN-49's didn't come with monte carlo stocks, particularly left-handed ones). Honestly, your best bet at this point would probably be to try a 30-06 stock as those seem to be the only ones widely available. Some minor fitting might be required (mainly the buttplate and hardware) but it shouldn't be too big a hassle.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar