I couldn't find any evidence of this recording anywhere online. It's not even listed on Discogs, although it may well have been recorded around the time of these four other collaborations by the Qawwali cousins.
UPDATE: WFMU legend and Give the Drummer Stream Artistic Director (aka my boss) Doug Schulkind found that the three tracks on this cassette also appear on 1978's Supreme Collection Vol.3.
So this recording dates from more than a decade before NFAK would achieve international stardom.
Instrumentation is sparse: tabla, harmonium, hand-claps, and two of the most expressive voices ever committed to magnetic tape.
The recording is breathtaking, with an earthiness more akin to David Toop's description of Lahore in Exotica than the singer's later collaboration with Eddie Vedder or the Massive Attack remix.
Get it here.