There is a problem with the upgrade. There is no flash memory chip in the BL7000, it's a smd 27512 Eprom. So upgrading means removing/destroying the old chip and soldering a new one on the board.
But even this is not recommended. The cpu boards a different, there are at least 2 different layouts of the boards and probably the new Eprom version will not work.
But it is possible to replace the complete cpu board, the rest is compatible. A V1.3 cpu board can be replaced by a V3.1 RDS and will work. Tested.
What's on the cpu board? Really? 80c32 cpu, 6264 8K CMOS ram, 27512 Eprom, some CMOS decoders, 3025 Lithium cell...