David, XHP-260 and HP260 engines would be tough to cover in little text boxes. Cylinder heads were prototype racing casting used in no other engine. Everything in those head assemblies was unique to them and not based on any other engine. In all these decades I have seen one pair not in an engine. Connecting rods were prototype race forgings and assemblies. I have seen five not in an engine, the XHP-260 camshaft was a strange Ford/Sullivan/Potvin creation that cannot be cut from any other Ford design, the HP260 camshaft is what the HP289 was later based on. So on and so forth. Evidence suggests that only 35 each XHP-260 engines were built. At least 137 each HP 260s were made and probably more. Ford spent hundreds of thousands of dollars making the small numbers of racing 260 engines. I know of one XHP-260 and one HP260 still mostly complete in original condition.
Aluminum case transmissions did not arrive until CSX2136-CSX2138 were being completed.
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