Yes, the 401 is the longrail version of the 400. I THINK I have a 401. It has a 24" extension which I think makes it the 401. And it is a "Grey Ghost". Although ghosts aren't supposed to weigh that much!
I'll probably end up repairing it. It is a very nice camera. I bought the whole thing for $150 including two Riteway film holders still new in the box. Tomorrow I HAVE to call Calumet and get that part! Been putting it off for too long.
I must say though it is a great studio camera. It even is stable on my Gitzo 3038/Benbo Mk2 which surprised me. I thought it might be too heavy.
As for lenses....
IIRC the 401 takes a standard 4" lensboard and I THINK you can easily get a recessed lensboard if needed. Plus you can get out on the end of the easily. No problems with a bed showing. I can't imagine that there is much you CAN'T put on that beast if you have recessed lensboard and are out at the end of the rail.
That said I'm sure someone has made a 20mm lens out there for 4x5....