I decapped and visually dumped the ROM from Mattel Computer Gin's NEC D650: http://www.seanriddle.com/necucom4.html
The bit layout on the D650 is the same as on the D553 and D557 (and probably the D546).
I compared the visual dump to Kevin's electronic dump, and noticed his dump had bit 5 stuck high. But pages 1, 5 and 7 are completely different.
Tigrou from Belgium sent me a Tandy Pirate to de-glob. The PCB had a few hints; buttons were marked K1-K4 and S1-S4, and it used a single 1.5v coin battery. Looking through Bitsavers' data books, the OKI MSM6051 looked very promising; the chip was wired up almost exactly like the example application diagram.
But after I cleaned the die, it turned out not to be the MSM6051. It doesn't even have a manufacturer's name or logo, just the label 3C5800-919. It turns out that Travis Goodspeed had posted a 3C5800 die shot from an RSA SecurID. Unfortunately, I haven't found anything else about it. Worse, the bits aren't visually discernible.