The '76 wiriing system is not like the earlier ones. Current paths are divided up on the engine side of the firewall. So if your car is stock - no electric pumps or fans, no electric winches or anything like that, the only issues may be those related to aging. Those will depend on environment.
Offhand, I don't know if the headlight wiring was beefed up from the years which used 16 and 18 gage. Regardless its a long path and that circuit that can be improved with a relay system.
One thing to be aware of with LED lamps. Often they have a more concentrated pool of light. With something like a dome light, where its desireable to diffuse the light over a wide area, it may or may not do what you want. May have to try a few to decide. One with the correct design to work with the reflector and diffuser.
How the dome lights work:
Power is connected to the socket at all times.
The return side consists of multiple wires. Each one is connected to a switch to chassis ground. Closing any one of those switches completes the circuit.
So if your LED is in any way touching ground, it will not turn off.
