I wrote an article on this exact subject that was printed in Power Wagon Advertiser a couple months ago. Some of those engines had regular 6 bolt cranks, some had the extended flange 8 bolt crank. If you remove the 8 bolt crank, you can drop a regular 6 bolt car crank in its place. There were both 361s and 413s done like that. I wrote an article on this exact subject that was printed in Power Wagon Advertiser a couple months ago. As for the ductile iron rockers, I've seen them on the marine engines, which are the same block as the IND/Truck engines. The heavy 413 blocks can often be bored .070" to standard 426W size, and that is why many nostalgia racers and Max Wedge guys always look for them...