This is a unique Hal Hosterman design that uses ball bearings inside curved tubes to replace the traditional OHV rocker arm assembly. ​Hosterman started making these heads around 1926, producing 1500-2000 over several years. He sold them, with a special exhaust manifold, through various distributors including Montgomery-Ward.
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   Hal recounted later that he and his hop-up friends, in their 'T's equipped with these heads, would wait at the foot of a hill in town for owners of big cars to start up the hill, give them a 'third of the way' lead, then take off and pass them as though they were standing still.