Well, I must be in a kind of a disagreeable mood today, because I'm about to disagree with everyone here.
First, I'll disagree with Ken about the idea that a long scale concert should be thought of as a Tenor. It does have that scale, but it's the size of the body that determines what will sound good. The smaller the body, the higher you go with your tuning.
So that brings me to my disagreement with most of the rest of the opinion - that a low 4th tuning is a good idea on a concert body. Not just a long scale concert, but
any concert body. The wider the spacing of notes, the more a big body is needed for them to resonate properly. This is why re-entrant tunings were invented - to space the notes closer together for a small bodied instrument.
Of course there are a lot of people who like an unbalanced sound anyway.
SailingUke
The unwound G ... totally booms.
You may have a playing style where a booming 4th helps out. Yes, I know Ohta plays a low 4th concert - it works for him and maybe it can for you.
Still, we love long scale instruments in general (almost all we build is done in this fashion) and this configuration in particular. It allows you to use lighter gauge, brighter strings than on a standard Concert and you don't need as much tension as a standard Tenor because of the smaller body.
Our favorite tuning is a B flat high re-entrant. These notes are a perfect fit for a concert body. The sound is rich and full. If you need to play in C tuning sometime, the other great advantage of a longneck is that with a capo, you can "capo up" to C, and with most instruments, still have as many frets to the body as with a standard concert.
With us, we especially like the Soft Medium set (or standard Medium for brighter) for that set-up, but in fact it's really easy to do with anybody's strings. As Ken said, get Tenor strings - but a high re-entrant set. Then just slack the tuning down to B flat. As mentioned, you don't need the tension on a Concert that you do on a Tenor, so this works like a charm.