As Don said, its not advisable to just randomly swap main caps unless you have a dial bore gage to confirm they actually fit that main saddle. You should take it back to the machine shop so they can verify that the caps are not in the wrong position and number them for you. Unless you numbered the connecting rods and caps, they should check them and number them for you as well. Plastigage is only good for checking the clearance at the exact spot you place it on the crank journal, it cant tell you what is happening at other places around the housing bore.
