Abalore (look for his Youtube channel) is not at his first Amstrad production (see below), and today he is at his best as he made a simple electronic interface adding a cartridge slot for the plain Amstrad CPC (464, 664 and 6128) which can only be used normally on an CPC+ or the GX4000 console.
Beware, it doesnt add magically the CPC+ features. But it's the key for games with a monstruous size up to 4 Mb with a simple memory banking.
And you can also use it on an CPC+, the internal cartridge with Burning Rubber or basic is still usable, the Plus2CPC will let you load games or another operating system.
A file to be used with a 3D printer is available on his web site (see above). He can make a version with edge or centronics connector, or MX4, v3 without reset button or v4 with reset button.