Looking at the book, looks like just NSR cases with NF5 barrels. There is also 78PS quoted in the Japanese text. So not much MC28 left except for the frame & swingarm.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30