what size is the head stud threads etc for 24 stud v8 merc

[ajmac]

You can get a more reliable torque with the studs as the nut end uses a finer thread than a cast iron block can reliably take, the block end is UNC and the nut end UNF. Also back then heads were off once a year for a decoke unlike with modern fuel additives where you don't strip and engine unless there is a failure.