From my understanding there were two ways of counter
rotation. Custom Ground cam or a gear drive two spin the Camshaft the original way.
The distributer gear is ground different to keep the distributer and oil pump spinning the same way.
The firing order on this custom grind is opposite of STD chevy. 12756348
All reverse rotation engines have that firing order, and in saying that with a belt drive, timing chain, or three-gear(idler) the cam has to be ground specifically for that application so that the cam and crank both turn clockwise (as viewed from behind the engine). In this case the cam gear and distributor gear are ground to turn the distributor and oil pump in the standard direction.
the two-gear timing setup used in stock Merc counter-rotating engines spins the cam in the standard rotation while the crank spins in the opposite direction, allowing a standard distributor gear to be used.
So to Answer your question the differences would be
Depending on what method used to counter.
1) custom ground cam shaft
2) Distributer gear
3) three gear Idler (no Timing chain)
4) Rear main Seal
My guess is the Failure of your engine has nothing to do
with the counter.