Sounds good. Let me know when you're done and I'll paypal you return postage.
The Hitachi chip is from Mattel Armor Battle. The stenciling under the IC socket I installed lists 2 similar part #s, one for Armor Battle and the other for Sub Chase, so it might be a standard MCU that's just labeled with Mattel's part #.
When I get them back I'll torch them all and map the bits in the MM7x and D557 ROM arrays to your dumps, and see if there are any hints on the other 2 dies.