John Kirkpatrick played Mattheson's Gigue (not Bach) on Jump at the Sun. The original was in E minor (I have a printed copy) and he transposed it to A minor to fit the range of the instrument, and made some small tweaks to make it playable.

It is indeed a 4 part fugue, played and recorded (as the sleeve notes on Jump At The Sun are at pains to point out) without the benefit of multi tracking. He re-recorded it on the Anglo International CD set released recently.

I tried to learn it once. With practice I could get up to and including the entry of the 4th voice. As I was also transcribing it from a recording, it got too difficult after that. Not only 4 parts but it starts getting harmonically complex from that point onwards and I just couldn't work out what all the notes were.

Anahata