@dc42 The MKS mini unfortunately no, they have a history of not being very friendly in that regard, I did find someone had posted the level converter ic being used is the same 75hc4050 used on the RepRap Full Graphic Smart Controller and its also used on the Viki2.
The reprap wiki lists this pin out for the MKS Mini https://reprap.org/wiki/MKS_MINI_12864
Annoyingly they didn't put the lcd CS pin in the same location as the RepRap display so that would require additional custom wiring. Interestingly they did not put in separate SPI signals lines for the LCD, they are pulling from the SD card SPI lines. To me this suggest that the 74HC4050 is being used to shift the SD card signals as well as the lcd signals but as I do not have one of these displays I can not confirm how the lines are being level shifted.
A person could use use the "dupont" style female - female jumpers instead of the ribbon cable on the EXP1 header connections to make the custom connections if they did not have access to crimpers and a selection of Molex SL series connectors/contact pins to allow for crimping custom connectors.
Panucatt Devices list them selves as being an open hardware company but like you I was unable to find a schematic for the viki2 but there is a wiring diagram available to aid in hooking it up http://panucattdevices.freshdesk.com/support/solutions/articles/1000158562-viki-lcd-2-0-support-files .
Perhaps they might provide the schematic if asked for it, I didn't think about doing that as i was able to work out the needed info from the Viki2 I have in hand.
I looked over my Viki2 and did some quick pin tracing and the 74HC4050 is being used to level shift all the signals and is using a 3.3v VCC into the chip as the display is 3.3v as is the SD card. I looked at the data sheet for the 74HC4050 and it indicates that it will recognize a 2.5v+ signal as a high signal when 3.3v is used for VCC, given that, no level shifting is required for the extra A0 signal that is needed.
The Viki can be setup to accept 5v or 3.3v on its VCC input line, 3.3v is passed through directly and 5v goes into a voltage regulator to produce 3.3v.
The Viki2 also combines the SD and LCD SPI signals together like on the mks mini.
Given that the Viki2 has its own custom pin out for the connectors I had planned on making my own custom cabling to hook it up to the Maestro.