Granted using separate throws for the rods would have been best for more of a ideal firing sequence and balance, but if you use the original crankcases then you are constrained to keep the original crankshaft with its finite length of crankpin. So the rods would have to be more thin for both to fit. In this case using the knife and fork rod setup is a reasonable way to do it. But I think that using a master slave rod design would offer stronger rod strength and less wear at the critical crankpin end. I have seen flat twin engines and V-twin engines using the master slave rod design before, but I don't remember where at the moment.