Jeremy I have no idea about the relevant costs of an M20 or 16H head, other than there are probably 10 times more M20's existing now than 16H's therefore more demand for spares??
Regarding Torque Wrenches. They were a crude spring pull device back then and not in general use in ordinary workshops. Hence torque wrench figures are not included in the manuals. They were tightened by experience and even different length spanners to adjust the pull.
Figures today are quoted either from experience or by comparisons from more modern vehicles with a similar fitting or charts giving figures for different threads and sizes etc.
The biggest culprit of blown composite head gaskets is after fitting a new one, failing to re check tighten the bolts as many times as required during the first warm up sessions until it is compressed to it's maximum. Even then, the cardboard in the modern gaskets will still often blow out. Ron
The numbers could be it, but try finding an ally head. They seemed to have been binned when replaced by iron ones. Sidecar outfits were owned by folks that generally couldn't run to a car, not keen mechanics
