the previous owner put a new 305 rebuild in, so that explains the incongruous motor. I'm not worried about the accessory brackets and radiator so much as the actual engine-to-frame mounts, but it's good to know about the external balancing...are there any internally balanced big blocks? I would prefer a 366 or 427 tall deck truck engine, but they're harder to come by it seems. The radiator is definitely too small for a big block. It's a Spicer 5-speed by the way.