My V40HL is the 16MHz version and I am going to try run it at 20MHz or 24MHz.
doesnt really matter, keyboard controller is sitting on 7MHz ISA bus, what you need to worry is access timings
READ:
CS, A0 to Data Out Delay 130 ns
tRD RDvto Data Out Delay 130 ns
tDF RDuto Data Float Delay 85 ns
WRITE:
tWW WR Pulse Width 160 ns
tDW Data Setup to WRu 130 ns
8042 handles this with dedicated hardware slave port, what you might need is a small cpld to handle the bus and buffer I/O, or one of those fancy microcontrollers with buildin cpld block, or something with really fast realtime IO like XMOS