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The problem with trying to straighten a connecting rod is that you will have great difficulty getting the wrist pin hole truly parallel with the crank journal hole. That could cause excessive bearing wear as the piston tries to twist in the sleeve on every stroke. I am assuming you mean four v-blocks on snug fitting shafts through the wrist pin and crank holes. That will only help you get it straight in one plane. How do you propose to straighten it the other direction (shafts closer at one end than the other)? As you start straightening, residual stresses in the rod will cause uneven springback twisting the rod in whichever way it wants to go. I expect after your first bend on four v-blocks you will be only touching three. You have to keep over-bending it different directions (or different planes) to keep removing each new distortion. It will take large accurate calipers to figure out how it is bent and to finally get the holes straight. We once straightened two cylinder rods which were bent 15 degrees or more. After three or four tries on the first one we had a corkscrew. This was not visible to the naked eye, but was detected with dial indicators as the shaft was turned in v-blocks. Several hours of sketching the shaft and carefully overbending in the right direction up and down the shaft finally got it to ASAE specificaitons. We'd been money ahead to buy new shafts. The second one went better but was still not easy.
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