This lists everything that goes wrong with pistons with pictures and probable causes. http://www.mlcmotorfactors.co.uk/Trouble Tracers/PistonTT.pdf
Likely as not there was an air leak that caused the head to crack... that then lead to total failure... but it also depends on how the rolling road set up the engine... some places have a habit of setting up engines for economy, so generally they're running on the lean side of things... You can often hear a cracked head, as it'll make a slight hissing noise... just added that as an fyi
No.3 only every ran hot on s/p engines due to the oil cooler being inside of the fan housing!! Early dizzys even had an adjusted points lobe to compensate for it too
Might have thrown you with the above pic, thats an old engine I stripped down and used the case off, just thought it might have been what the OP might have found. Twas a SP as I remember.
