Richard, I just measured my 1640. The length and width at the feet is approx. 54" x 20". The bolt-on holder (I store my knock-out bar , wrench, drive center and live centers in it) on the left end (you can see it in photos of the lathe) adds about 4 " to the length.
If you place the headstock even with the left end of the bed, the motor extends past the bed by about 12". Obviously, due to the sliding headstock feature, one can move the motor to where it is even with the length of the bed, if needed for space.
The headstock with the inverter is about 16" wide. The inverter hangs off the back of the headstock, adding width to the bedways. If you need more measurements, let me know.
By the way, I hold a very high opinion of the 1640.