I would recommend no faster that 2400 baud. Also remember that
you are limited by the amount of memory the kaypro has.
Try the following
On the windows pc convert the files to intel hex.
Connect the computer via the serial ports
on the kaypro type
pip file.hex=rdr:
With luck this will cause the kaypro to record input from the serial port and save it to disk
On the pc run a terminal emulator such as teraterm
Sent the hex file created from the terminal emulator
When finished type control+z into the hyperterminal this should release the keypro console
then on the keypro use the command
load file
To convert the file back to binary
you can then delete file.hex
This is a quick summary
There is also some information in this video
https://www.youtube.com/watch?v=32oxnyERDgI
Hope that helps