I purchased a Gulbransen player organ around the same time: 1979.
However, my model uses a cassette player; using the cassette player
you can record and playback.  At that time you could also purchase
cassettes already recorded by a professional organist.

The cassette player actually plays the organ electronically.  In other
words, what you hear when playing the cassette in the player is the
actual organ, not recorded audio music.  You can change the stops,
volume, vibrato, Leslie speaker, etc., while the organ is playing from
the cassette.

I used to use the cassette recorder to record one hand of a particularly
difficult piece.  Then I would play back on the cassette while playing
the other hand "live".

Larry Wilson