[Dave in MN]

I have a method to check the rear mains for excessive clearance without removing the caps. It is not highly accurate but it will point out abnormal movement and prompts further investigation. This is done while a car is on a hoist although it could be completed while on floor jacks.
(It would be a heck of a miserable job though when on floor jacks.) When I have the pan off the bottom of a car for a bearing check, I have often placed a sensitive dial gauge with a magnetic holder on the pan rail and placed the tip of the gauge on the crankshaft as close as possible to the bearing being checked. The crank needs to have the throws straight up and down. Using a tall support jack with a foot lever, I am able to apply a varying lifting force to the crankshaft. Because of the weight of the crankshaft, the crankshaft journal is typically in its lowest position in the bearing less the oil film. (But not always....) At times, I need to pry down on the crankshaft using the pan rail as the fulcrum to fully check the clearance. The dial gauge will show the movement of the crankshaft journal within the assembled bearing and that movement is the clearance less any residual oil film I find this method is accurate enough to confirm excessive clearance. The test actually works pretty good. Sorry no photos at the present time but next time I'll take some of the setup.
Good Day!