[Ron Ramirez]

The transformer on the 39-55 is mounted externally (top of the chassis) and is labeled Philco 32-7997N. I'm assuming that the "N" reflects the external housing.

Ignore the "N," the 32-7997 is what's important.

If I purchase the replacement transformer you suggested and hook up to the secondary terminals 1 and 4, which terminal would be used for the center tap?

See my first post in this thread, above.

That is not a center tap on the output; it is a feedback tap, meant to provide degenerative feedback to the audio circuitry as a means of reducing distortion.

I can put together a workaround for you, but I frankly do not have time right now...I'm up to my eyeballs in college work.