Don't grind the rivets. Those hubs are a tapered keyway type, similar to early Fords. The center nut holds them to the axle, and the whole assembly comes off as one unit. You need a special puller to remove them properly. Otherwise you WILL screw some stuff up.
If you have access to a decent tool crib or a truck it is worth it to buy a good one, especially since you own a early Mopar. They are commonly referred to as hub pullers. Here is a pic of one from Matco -
If you can't find a good one you may get lucky with a Chinese cheapie. You could probably find one at HF, if not they have them at AutoZone - OEM/FWD Hub Puller part #27037.
IMPORTANT STUFF: When using a 3-legged type puller on these axles be SURE the end of the bolt is FLAT. If it comes with a point, grind it flat! If you don't you will split the axle and then you will
really be screwed. Remember to adjust the brakes all the way off, so they won't hang on the drum. Also, run the axle nut out to the end of the threads, flush with the end and use that to press on. Not only will it protect the threads on the axle, but it will keep the hub/drum contained when it does break loose. They can and will take flight at high speeds, and you don't want to be in it's path if it does. Lastly, don't be afraid to use a some heat. A little persuasion from a hot torch will go a long way.
Good luck...