These are now single boards, with the keyboard integrated into the main board. The is a keyboard overlay PCB with keywords as appropriate for the system, and the optional ZXpand board which is soldered onto the edge connector.
The Minstrel 4th is 'designed for RC2014' and can be expanded via an RC2014 bus connector, to make use of all sorts of existing expansion cards.
All of those kits are available now from the new 'Tynemouth Software DIY Computer kits' section of The Future Was 8 bit - https://www.thefuturewas8bit.com/shop/tynemouth-products.html
Along with the Mini PET of course.