Don't know the specific answer to your question, but there were small and large journal 181 rods. Been 10 years since I rebuilt my 181, and not sure if there was a difference in the rod width, but the diameters are different. (I have the large journal engine, 1973 181CI 140HP....) Far as I know, the main bearings are the same, just different sized rods and rod journals.
Are the rods so messed up that they can't be resized?
I bought a engine rebuild kit from Green Bay Parts World, but other internal engine parts like rockers, water pump pulley, etc, from an automotive engine 68 ChevyII 153CI. Some of the parts even had the GM P/N stamped on them. External engine parts (pumps, electrical, ignition, fuel) have to be marine, no auto parts can be used.
FWIW, one of my cam bearings was oversized, from the factory by the looks of it, rear cam bearing. I had to run to the machine shop to have them cross it to something that would fit...