In order to come up with 10:1 in a stock M42, you need just under 50cc of combustion chamber volume...all the bits. The S52 has ~6cc more piston dish but more displacement.
1796cc at 49.5 cc's = 10.1
1958cc at 55,5 cc's = 9.8:1. That does not factor in the deck ht. of the S52 piston 31 mm pin ht. vs.30.4 of the M44 so you gain a couple tenths on the positive deck ht for a touch over 10:1.