Ok I'll try and explain the character generators without confusing everyone.
The 3001 and 6670 are industry standard character generators which mean that each character is in a specific slot. POKE 65H and you get a capital A, poke 97H and you get a lowercase a
The capital characters are compatible with how Steve L designed the video memory section of the computer, but the lowercase aren't Since the bit required to display them is missing, RS decided this was OK. If you replace the missing bit by adding a 2102, the missing corresponds with another slot on the character generator, so it displays a special symbol. You can add a gate and some wires to re-arrange the slots back to be compatible with the industry standard, and that is how DB-K and others get access to the lowercase characters already in the 3001/6670. NOTE, this was NEVER done by RS.
When RS decided they needed to offer a lowercase mod for the M1 they found that if you put the characters in non-industry standard slots, then you can get by just adding the 2102 chip. So the RS lowercase mod never uses the 3001 or 6670, they are removed and replaced with a 6673 or 6674. This allows RS to standardise the mod across all M1s. A fair number of late production M1s already have the 6673 and the 2102 Z45 is already socketed so if someone asked for a LC mod to that computer, the tech to do it as fast as I can make a coffee.
Clearly in Don's case, the 2716 Eprom has the code from the 6674 burned into it which is why it works with the simple RS 2-wire 1-cut piggyback mod.
Cheers,
Ian.
