The carrier is going to stick out past the 4' extension another couple feet for the bike to clear behind. That's the nature of a receiver hitch bike carrier. So you should consider that the bike proper is quite a bit more than just 4' out from the hitch.
There will be considerable wobble with that much extension no matter how tight you make things. A trailer has it's own suspension but a 600' load now at least 5' and probably more, past the receiver will be moving with the motion of the truck.
One other solution is to put a front receiver on the truck and carry it there. I did that with a 500 pound bike;
