Is there a part number for 10, 20, or 30 under bearings?
The main bearings are replaceable. The connecting rods are Babbit-lined and must be exchanged for rods reconditioned and re-cast to a smaller diameter if the crankshaft has to be reground. If the shaft is round and straight and the bearing material isn't deteriorated, the rods can be adjusted to the right oil clearance by removing shims between the rod and the cap. It is possible to bore out the rods and install an insert type bearing on the 48-53 216's. The rods from 1936-1947 or so were wider than the later models, and I don't know if a conversion bearing is available. for the earlier rod.
Jerry