Just for curiousity sake,I drew several crankshaft cross sections up in CAD, just to see what different engines have for journal overlap. The worst being the 292 crank,with only .138 thickness. On a cast crank, I dont feel it would be a good choice to try and offset grind the journal for more stroke, or even turn it down to a smaller journal size to accomodate a different rod size,further reducing the overlap more. A 235/261 and GMC are very good candidates for this type of mod. Because they both have very large OD mains relative to the fairly large rod journals. Plus there progressively larger main size front to back increases the overlap as the you go toward the rear of the engine. At a minimum, with the smallest main journal, the 235/261 has over .500 of overlap. Lending itself to the possibility of either offset stroking the rod journals or even grinding them down to BBC or SBC size and still having plenty of strength and integrity left in them. The 235/261 and GMC's being steel also is a good foudation for attempting to do this as well. Im going to use some BBC journal size H-beam rods for my project, and even with the most realistic HP levels and RPM you could ever expect to get out of these engines either N/A or blown, you'll never have any problems....even with just 4 mains!
