[Al_The_Man]

I am not sure of your question, you seem to have identified the wires ok, If you don't have any info on the encoder, and in the fact there does not seem to be any identifyable electronics on board, you may have to hook it up initially with 5v and see what the results are on A & B, hopefully it will be squared up and not a sinewave output. As regards transitioning a ribbon cable, usually you can split the ribbon conductors and solder almost any kind of connector on, rather than replace the ribbon which generally goes to a ribbon header in the encoder.
Al