The 351-C has smaller mains than the 351W, 400-C or 351/400M. This reduces friction (less surface area). Very rarely has a crank broken, so the small diameter is not an inherent design weakness. In fact, the 390, 427 and 428 all have the 2.749" main journal diameter. Note that no other crank interchanges with the 351C, even though all the 90 deg. V and 335 family engines have the same bore spacing.
There isn't really much exciting about rods. There aren't many interchanges
or alternatives. Here are some basic specifications. The 351-C rod doesn't
interchange with any other, and you can't stroke a 351-C using a stock
351/400M or 400-C crank.