Okay Paul.  I’ll take a nibble at this one.  As far as magazine articles go, this one had more information than is usually supplied but still lacked some critical assembly information such as bearing clearances, piston to wall clearance, ring end gaps, and exactly at what intake lobe centerline the camshaft was installed.  But also included were some blatant errors in the writeup thereby taking away some of the credibility.  Errors include: the number of links between dots for the cam timing is listed as eleven although the picture in the article shows twelve and the last year of production for the Y is listed as 1962 although its pretty common knowledge that the engine was used in the trucks through 1964.

But regarding the compression ratio, if the stroke is increased to 3.600” with a 3.800” bore, then the compression ratio with a 66cc head and the pistons at 0.023” below the deck will be at the articles mentioned 9½:1 with a composition head gasket.  The article didn't mention specifically that the heads were milled but calculations on my end with the article stating the the pistons were 0.023" in the hole indicate that the heads would be milled about 0.020" to get the CR to 9½:1.

The engine peaking out on power at 5200 could be the result of several things but the camshaft being advanced heavily would be at the top of my list if that's all I had to go on.  But then at looking at their graphs, the rpm scale stops at 5200 rpms with the power levels still climbing.  The dyno pulls were either stopped at 5200 rpms or the data simply wasn't included.