Couldn't you just as well run newer heavier gauge wiring to you rheadlights and do the same thing without having to add more stuff to your car and what about the brake lights they are dim as crap too.
Don't forget about the 40 year old stock switch. If all you do is run larger cables to and from it it will be the bottleneck for current. And since the circuit breaker lives in there, you may get the infamous flickering headlight syndrome.
I only say that because it would be as much or more work to run the heavier cables, and you may still have problems.
Honestly, all I did was cut the short wire that goes from main harness to the headlight on the passenger side. I wired the low beam side to one relay, the high beam side to another relay.
Then I took my heavy wire (I think I used 10 ga, if memory serves) and ran it from the relay to the socket that I removed from the other end of the cut wire. I bought a new socket for the right headlight and did the same thing (low beam relay operates both lights). Ditto for the high beam side. I ran a ground wire also from the headlight sockets to a good grounding point (this is optional but insures good current flow).
Then just run a FUSED full-power source (I'm coming from the battery side of teh solonoid) to the relay, add a ground for them, and you are set.
To go back stock, all I need to do is remove the relays and my new "wiring harness" ('cause I taped it up all pretty like), replace the stock short wires from the main harness to the headlights, and I'm back to the old. Not that I plan to do that anytime soon.