OK, finally had time to look at the other photos of this unusual Corn Exchange Jackpot. You can see there are two slits to the front side of the 2nd jackpot payout tube. This has to be so the exact number of coins in the Jackpot could be counted through the front glass, otherwise the Future Pay payout system used in this game would be pointless to counter the law.
The idea of these games being that there was no gambling if you knew ahead of time exactly what the game would pay. They did this by showing the winning amount in a small window but only allowing the payout to happen at the beginning of the next coin cycle.
The alloy coin chute that feeds the 1st standard payout tube only moves slightly on all the Exchanges I've had and not enough to reach the other jackpot tube without some kind of missing mechanism. But I don't think it ever did because you can see that tube #1 has an overflow channel cut into while the #2 jackpot tube does not. This implies a hand loaded jackpot.
The reason for two cups is fairly easy to answer as these are very narrow cups and even a win of 9 coins tended to fill the whole thing up, any more coins would have caused huge jams. I'm sure this was a later re-vamp to an original single cup game, so the easiest thing to do was just place another cup right next to the original. If this was an original design they'd have cast a suitable large cup to handle so many possible coins. The first cup appears to be exactly where they always sit on a standard model.
But what perplexes me is the added mechanism (sadly appears incomplete) that is attached to the inside lower mech frame just above the handle? Some kind of vertical sliding bar with multiple holes in it. I'll bet this has something to do with all those screw holes in the jackpot window, but what for? Maybe someone on the forum purchased the machine? Went very cheap I thought.
Also had a little think about how the jackpot slides could work since they are attached to the original payout slides. And you didn't want any coins being paid from the jackpot tube on a 3D or 6D win, which would have happened if this was the same as the standard slide setup. So the two lowest slides should be open below the jackpot tube, but the top slide had to be partly covered to hold all the coins until a 9D jackpot triggered, then the tube emptied. This also allowed the two slits in the jackpot tube to show all the coins that were to be won and be lawful.