Terry I would say that it is almost certain that the N-1200-E dividing network is original to your loudspeaker. Here's my logic... the field coil Duplex model 601, built immediately before your early 604, used an N-1200-C network, as listed here in the 1943 Altec Lansing catalog:

http://www.lansingheritage.org/image...943/page04.jpg

Note that the page was rubber stamped "Cancelled- see insert." This was because the 601 had just been discontinued and replaced by the 604. We are now probably in 1944, and Altec had not yet revised their catalog, but they had produced their first single sheet, two sided flyer on the new 604 as a "stuffer" for their still-in-use 1943 catalog. The two sides of this flyer appear right after the 601 page here:

1943

The first side of the flyer begins with "First Time In History." On the second side, note that it says "Dividing Network Crossover 1200 cycles." The only example of this catalog is the poor photocopy which I scanned for the Lansing Heritage site, so I am not sure whether the flyer was in color. Within a short time Altec would produce a fancy twelve page color catalog for the 604, also beginning with "First Time In History." In this catalog the crossover frequency is described as 2000 cycles, and the network pictured is the N-2000-B.

Now I'm not sure why the designation for this 1200 cycle crossover jumped from C to E, but the look, styling, configuration etc. is right for the period, matching the looks of the N-2000-B. From all the available evidence (including your apparently unmolested loudspeaker) it appears that the 604 was introduced with the N-1200-E network and changed very shortly after to the N-2000-B.

You can use my words in any way you see fit. I am one of the three co-founders of the Lansing Heritage web site, which along with 25c might buy a cup of coffee!