The FM16W08 chip used on typical NVRAM modules isnt quite identical to the normal SRAM chips but usually they work as a drop in replacement for most systems. If the replacement board is wired up the same way as the original Bally 6803 CPU it should work fine. Page five of the FM16W08 datasheet describes differences. https://www.cypress.com/file/41731/download
What NVRAM module do you have? On the NVRW ones there is a place to put a 10K pullup resistor on the /CE. It is needed for Midway arcade games to keep the NVRAM write protected at power up and power down or else sometimes the NVRAM gets scrambled or the board fails to boot. If the replacement MPU is wired up differently than the original you may want to try adding the 10K pull up to the NVRAM module if you can do a SMT resistor.