See the feature from Motorcyclist magazine (USA) in the attached pics, from 1991. It talks of an enhanced eight-valve K100 powerplant, rather than the 16-valve K1/K1100 series.

This one is up for auction in Brisbane, incorrectly listed as a 1978 model. In this case it's described as running a stock K1 powerplant. On its own, that represents a significant upgrade from the K100 unit.

Postscript Dec 18: Bidding went to Au$16,000 (US$11,400, GB£8600).

Another was listed for sale several years ago, and provides further background on the Martin/Brune ‘kit’.

See our BMW K1 feature.