[Nathan Slingerland]

The U-2 speaker is really heavy - you might be able to squeeze it in but I'd wonder how to mount it in a tombstone cabinet.

There's a good picture of the U-2 here:

http://www.tuberadioland.com/images/philco16x_10.jpg

The H-13 speaker in a 16B tombstone:

http://www.tuberadioland.com/philco16b_t..._side.html

The H-13 speakers are not all that uncommon since they were used in many models. In fact I have a spare H-13 speaker with a bad output transformer - it might be possible to swap the U-2 output transformer onto it. PM me if you're interested.

It shouldn't be too hard to convert a 16X chassis - not even sure if it's necessary to change anything. Perhaps someone else could chime in about the electrical requirements if you're interested in that route.

Best of luck either way.