I believe it was low compression because of the octane ratings of the fule used back in those days. Even though all k10's were built to run on un-leaded fuel, they could also run on 4-star (that's leaded for all you youngsters out there) which was 98RON i think. The theory goes; high compression engines make the best use of lower octane rated fuels. Hence why the MA10S (90' - 92') is more gutsy than the MA10A (83' - 89'). Before someone points it out, the MA10A isn't officially named "A". I just added the "A" to avoid confusion.
And just a little trivia for y'all, the origional run of face-lift k10's, built in June, July & August 1989 (The very first one's for the uk) were fitted with the lower compression pre-facelift engine. My GS special is one of these early cars, assembled on 18th June 1989 and registered on the 22nd. The low-comp motors used on these cars were dressed up with face-lift oil caps, altinators, distributors and expansion tanks. I believe the cam-belt sprokets were also changed for the later ones at this time but they might have been done earlier, not certain on that one.
By far the MA10S is the better engine.