I would have thought that somewhere in that hoard of information Owen found, you would find a user port tester program which will probably need a simple loopback connector to work.
Sending values to the user port will involve setting up PORT A of the 6522 to be all outputs (once) by POKEing an appropriate value to the data direction register for PORT A, (POKE 59459,255)? ...then POKEing the values you want to output to the data register for PORT A. (POKE 59471,value)?
This might make for good bedtime reading, although the example for outputting to the port is more complex than it needs to be.
http://cini.classiccmp.org/pdf/kilob...k%20(0379).pdf