Before Plastigauge, a small piece of .002" shim stock was placed between the lower main bearing shell and the crankshaft, the cap was torqued, and the flywheel was given a firm tug. If the crankshaft turned freely, a shim was removed. Once the crank turned with a moderate drag, the clearance was assumed to be .002" and the procedure was repeated for the rest of the main bearings. Babbit rods got the same procedure. 216's, early 235's and 261's had main bearings with dowels top and bottom. Midyear 1954, the upper bearing shells got anti-rotate tabs instead of dowels to make main bearing changes with the crank in the block simpler. I've never seen rod bearings with dowels instead of tabs.
Jerry
