Thank you for the pointer to the TekWiki resource. I have found and downloaded the two ROM files. I do have an AVR programmer and a ZIF socket board that can take up to a 40pin DIL chip but I'm not sure whether this can be used to read the MOSTEK ROM or write the 27C64:

https://www.ebay.co.uk/itm/AVR-Minimum-System-Board-ATMEGA16-ATmega32-USB-ISP-USBasp-Programmer-For-ATMEL/202959381564

I am happy to invest in a suitable programmer provided it is versatile enough to read/write a range of vintage EEPROPM chips.