Bought a pre-soldered kit but ended up getting a regular kit.
Update December 23, 2019: through-hole in the top case is designed for Alps not MX. Can't fit switches into it. F.
Decided to use a replacement controller that also features a ATMega32u4 chipset.
Elite-C v3.1 (USB-C Pro Micro Replacement)
This should be a drop-in replacement.
Purchased from SPACECAT for hopefully faster shipping but it's still slow.
Got 50 of these Mint Panda Switches.