IMHO I don't think this is a mod someone did, but possibly some strange short run at the end of the 777 series or even a one off. I just don't see how someone could cut a square hole for the single LED and the long rectangle one for the green round LED's. Also there is printing under the single LED which indicates it was silk screened at the same time as the rest of the tuner fascia.
I do agree that this is the same radio, just coming up again....Maybe it was a one off from the factory, a test radio. I was in the electronic's manufacturing industry for 13 years and these things do get created and never go into production. How it got into the world is anyone's guess. Possible created to test a feature that never went into production and ended up in the hands of an employee and then sold off and made it's way into the world.
Sound's strange, but we made incredibly complicated "One Off's" that cost so much in material's that they ended up on the manufacturing floor and were sold. They were test bed's for future of products. That's where I would put my money if I were a betting man!
Either way, it's a rarity. If you need that "Ultra Rare" box, just for the sake of being rare, this would be it.