It was fascinating to see that the Heppners definitely had dissimilar speaker cones. The right-hand speaker (viewed from the back) had a relatively flat, ribbed cone, while the left-hand speaker had a smooth cone that was shaped somewhat like the bell of a trumpet. The ribbed cone carries model number AO-24346-0, while the other displays model number AO-24347-0. Research indicates that this combination of speakers were used in Model L-100 and other Hammond console-style organs. The ribbed cone handles low frequencies while the horn-shaped cone emphasizes higher frequencies, thus creating an apparent cross-over where there is no cross-over in fact.
The speakers both had a light coating of dirt -- not just dust. I infer that they were not installed recently. It remains odd that someone would have replaced original speakers with relatively unknown Heppner speakers rather than more popular brands of speaker. If there was a modification, the person may have been aware that Hilgen amplifiers commonly used Heppner speakers -- or the originals may have been Heppners as well, which made the choice of replacement speaker more obvious.
Once again, I do not understand comments I have seen in Internet forums suggesting that the Heppner organ speakers sound "bad," especially for guitar amps, or can handle no more than about 10-15 watts. These speakers are matched with an amp having a power rating of about 50 watts RMS, sound wonderful, and show no signs of being stressed beyond their power-handling capacity. I suspect that speakers that do not sound the way some people expect them to sound tend to be deemed "bad." However, my hypothesis is that the fault lies with their expectations, and not with the speakers themselves. One could argue that Paul McCartney's tone on his Hoffner violin bass is "bad" because it does not sound like a Musicman Stingray. However, that argument is unlikely to be well-received.
If Heppners are as bad as they are reputed to be, it is difficult to explain why Hammond switched to Heppners from the much-ballyhooed Jensen speakers. It is unlikely that Hammond's marketing gurus aimed to decrease sales of their products by causing them to sound inferior to their earlier models and those of their competitors.