With electronic controls it should be very easy now to sync them.
Going back to WW2 some LCM's where powered with 2 or 4 6-71's tied into a common gear box and did they fight each other a little? Yes, but you could be close enough to make them work better than one engine but they were slow speed and reliability was the main reason for multi-engines on a sinlge shaft and not performance.
On diesels you have two types of governors load senseing or speed sensing. Speed sensing you tell the governor how much fuel to give the engine and if it bogs down you give it more throttle, exactly like a carburator does.
In load sensing you set a desired RPM and regardless of load the governor adjusts the throttle to meet the desired RPM's like a big CAT dozer would have.
The LCM's used load sensing governors so when the Capt. moved the throttle he set a desired RPM range and the engines adjusted themselves to meet that RPM. Today it's all computers, no more springs and flyweights!
On the LCM's should they loose and engine or two they could still complete their mission and get troops on the beach that was the main concern.