One issue you're likely to run into with new carriage bolts is the raised grade markings on the head, where the originals were smooth.
In my opinion this looks bad, so whenever I need a replacement carriage bolt and I'm forced to buy a new one, I chuck it in a drill and using a file and foam sanding block, I grind off the raised markings and then either clear coat or paint the head black.
Since you already have carriage bolts, it's easy enough to use the same technique on them, just without the file.
After sanding, use an awl and punch a line of holes about an inch apart in some thick cardboard, screw the bolts into the holes and spray paint them. You'll find after using the same cardboard several times, the holes will almost become threaded and reinforced by the paint
One last tip- you can also prepare the bolt and use a version of gun bluing, or black oxide to tint them closer to the original factory treatment. It's a little more work and requires some buffing of the end result.