After mid-year 1955, 235s have an anti-rotate tab at the parting line of the upper main bearing shells. Those mains can be swapped by loosening the other main cap bolts 2-3 turns. 54 and early 55 engines need the crankshaft to be dropped about an inch to change the upper bearings. That requires removing the harmonic balancer, the timing cover, and the transmission to get that much drop on the crankshaft.
Jerry
