Parts are easy to come by for the harness, although I don't know of any 4-headlight jeeps. For the headlights, practically anything with four headlights could be sourced, and the connectors for the lights are the same as H4 bulbs, just with a different wiring pattern.
The other major Eagle difference is the 3-wire tail lights as opposed to the 2-light pattern AMC used up until 79 or 80. Cherokees may help you there, it's the only 3-wire Jeep I can think of. (3 wire: Stop, Turn, Park; 2 wire: Stop & Turn together, Park.)
I would set up relays for the lights myself even if I replaced the switches. I'm doing that on all my older cars. The most expensive part is the relay & socket, or if you can pick-a-part the relays, just sockets. It usually nets 2-3 volts at the socket. Additionally, the high-power low beam lights are 40w/55w instead of the old standard 35w/35w, putting more draw on your system.