Help with hei install

If you don't want to molest the factory wiring, use a male-male spade to connect the blue and brown connectors together, or make similar from a short jumper wire.
Relays are good. I put a 7-relay underhood fuse box from a Jeep in my 60's Mopars. Got rid of the factory starter and horn relays, but I custom-wired all under-hood since my wires were old and brittle.