It should be pretty straightforward. You need to change the headlight connector to one for a 2 way (low/high) bulb. Then just move the wiring from the old high beam connector to the high beam side of the new connector. The new connector will have 3 slots vs 2 on the 1 way lamps.
Using the relays you still will need 2, one for low and one for high. The problem is with the wiring and the voltage having to go thru the headlight switch, etc. See the link above, look for the headlight relay in the tech section for more details.
Damn, I am going to be doing the same thing on my 70. I saw the Spectre dual snorkle setup at a Pep Boys this last weekend. Just about like the old Ford Thunderbolt system. If you use them, or even not, go to their website, they have the piece to replace the headlight stuff and hook up the hoses.
I am trying not to get locked in at work, if you have any more questions I will try to answer them tomorrow night.