You can predict most MPxxxx MCUs by comparing it with this table at the start of this MAME driver:

Do you know the TSI Speech+? It's a talking calculator for the blind, it has the same speech chip as in Berzerk(arcade game).
*TMC1007 TMS1000 1976, TSI Speech+ (S14002-A)
*MP0057 TMS1000 1978, APH Student Speech+ (same ROM contents as TSI Speech+?)

I've been told the speech ROM is already dumped. The calculator is very expensive on eBay and it would be a shame to decap the MCU on it. Maybe someone that owns one can send it to you or kevtris to try to dump it electronically?