Using a plate mounted nitrous set up on an early style stovebolt probably runs into the same issues as trying to use throttle body efi on an early stovebolt, The Siamese intake ports. Very likely to have the additional fuel injected to support the additional o2 released during nitrous burn puddle in the intake and cause a lean out, and then a melt the piston event, in addition to the rod issue identified by HRL.
