600 RevD suggestions:
1. Remove the keyboard and use 542 keyboard.
2. Three 28pin sockets for ROM. ACIA selectable at E000 or F000. MON 8KBASIC 8KPremier TKit BV BX etc
3. One 24 pin RAM/ROM
4. Remove the 2114 RAM sockets. Square up back corner of board for circuit usage.
5. Minimum 40K PAL decoded bank selectable 2* 32 cache RAM
6. 64/32 column selectable video
7. Plug in 630 colour board
8. Add AY3-8910 and PIA for sound and I/O (I have working design and software)
9. I/F to 48 pin bus for I/O expansion and proto.
10. Baud rate generator
11. 1 / 2 MHZ selectable
12. FDC data seperator (FDC9216 ?) dual drive sel motor on/off
I've already committed to 2 sets of keys and 470 etc but just don't fancy using a standard RevD (or standard 502 for a C4 system) and not interested in 610 board at all. Wish to do most of above with 502 board also later.
There are existing circuits for most of the above it's just a matter of bringing it all together on one board and not having to hang bits and pieces off any repo board.