Conversion wiring

Think I may finally have the /6 sold. Fella was wondering if I was willing to part with the spark control and regulator boxes with thier associated wiring so he can upgrade his '66 to electronic ignition. I'm just wondering if I'm going to need the /6 harness when I slide a small block between the fenders or if it's completely different and should just go with a new V8 harness from Painless or some such. Car is a '74 Swinger. Are the spark and regulator boxes for a V8 different too or will the /6 pieces work? I'm thinking no but just wanted to be sure. Thanks.