Keith,
I'm not sure you can directly connect that AT-250 with a TS-440. With a TS-430, yes, but not the '440. If you happen to have the manual, figuring out the pin-out and purpose of each line shouldn't really be all that difficult.
Having had a '440, and I think I still have an AT-250, I can tell you that the built in tuner in that '440 will do anything the AT-250 will without the hassle of re-wiring anything. Nothing wrong with that AT-250, but it definitely pre-dates the '440.
- 'Doc