Checking Connecting Rod Oil Clearance

Plastigage is better than nothing, but measuring is best.
However, if it's all you have I commend you for taking the time to check.
Place the plastigage material on the center of the cleaned and dry upper bearing shell - that's the "lower" one when the engine is upside down. Then torque it properly in steps. It's critical the bearing and journal surfaces have no lubrication at all for this to be accurate. Then loosen the bolts and using the butt end of a hammer or mallet, softly tap the pin boss of the piston. It should pull the cap right off the sleeves and leave the plastigage intact to read. It's best if you mock up the lower end without the rings and do one cylinder at a time. You want to not have to rotate the crank since the bearings are dry.