Another update, and more questions...
I received the University Sound 1808-60 amp and it works great, the trumpet protect circuit seems to be the right low cut for these horns so I'll use that in lieu of my simple capacitor filters. I also found a spare 1828T driver on ebay for $40 so I picked that up as well. I took the transformer out when I got it since I don't plan on using these on 70V.
Now that I finally have 2 drivers and 2 horns, I got to do some playing around today, and discovered something interesting: it seems that there were two different drivers used in the 848 horns. The original driver appears under the "Drivers" section of the EV archives site as the "848HF". The EDS actually appears to be talking about the characteristics of both the driver and the horn at the same time, and doesn't give any specifics of the driver itself, but from visual inspection I can see that the 848HF has a larger diaphragm, and slightly different construction. Overall it is swappable with the 1828, as the threading and general mounting are all the same.
The really interesting thing is the audible difference, though. To my ears, the 848HF sounds more pleasant, at least with music playing. It has a little bit more midrange and less of the harsh upper mids that are typical of horn drivers, but it does have less high frequency response than the 1828. The 848HF also has more bass response (I know, bass response in a horn is kind of silly sounding, but it really does!). It really makes the 1828 in the 848 horn sound like a reentrant horn by comparison. The frequency plot listed on the 848HF is also markedly different than that of the 848A data sheet in the archives (under Horns, not drivers). Ideally I'd love to have a pair of the 848HF drivers, but it doesn't look like I can get replacement parts for them anyway, so it looks like I will need to get my other 1828 driver working so I have matching drivers in these horns. Still working on getting that stupid diaphragm washer I need. Darn $2 parts!
-Dan