I just read a question and answer in the July/August issue of Oliver Heritage. It talks about a 4440 four through six bottom which is semi-mounted like the 5540 and 5760. It also mentions a 4340 four bottom but is does not give information on whether it is trailer or 3pt.
I own a 4240 three bottom trailer plow. Going on this information I would infer that you are looking for a model number that fits in between 4240 and 4440.
I hope this helps a little more and does not confuse the issue.