300 km is just over 186 miles, I can see a well put together bike doing this as long as it is done at a reasonable pace, I wouldn't ride full out as fast as I can go for that distance, and Id have a few stops to check things out, like nuts bolts, wheels, chain tension and such, I've got several hundred miles maybe 600-700km without any significant maint. before, it all depends on how well the bike is put together and if it has been tested with a good amount of travel put on it so the engine is well broken in and proven to be reliable.
all things concerned in good condition and my answer to you is yes what you have proposed to do is possible.
700 km is roughly 434 miles.... now that would be a wicked long trip on a motorized bike.....LOL! Id be taking some tools and parts for that one, nuts, bolts, studs, gaskets... that would be a wild adverture for sure and great fun with a couple of buddies who had good bike also.