The only issue with using a relay to power the HEI is the relay. Do not use any of the Chinese junk that you see for sale on eBay and other websites. They look nice but are not durable. Use a good quality brand of relay and install it where you can reach it. Then keep a spare just in case of a failure. I have used 30 amp four pin relays with pretty good results and yes, I agree, easier on this old wiring, old style of wiring, and old ignition switches.
