The original rods for the early Aurelia engines are worthy of replacement. The conrods were originally sized for the 50hp 538 engine designed in the 1940s, and were unchanged in the early Aurelias. Perhaps adequate for a B10 berlina, they really aren’t up to a hard driving B20 s.2. As an example, my car was taken off the road in 1963, with a rod through the side of the block. It seems conrods were a problem back then too.
When Walt Spak rebuilt my engine in 2010 he commissioned new rods from Cunningham on the west coast. They worked closely to get the rods correct dimensionally but also strong. New rods will require rebalancing the crankshaft, as the reciprocating weight for the piston/rod assembly is now greater, it is also important that the rods all match in weight closely.
The new rods involved a few other changes:
FYI - I'd recommend looking at the valves too, especially for s.2 engines.Beppe Regazzone once told me that the s.2 valve stems were the same diameter as the earlier motors but were made longer for the new head configuration, and susceptible to breakage. The factory went to thicker stems in the s.3 motor, we made new SS valves.