Rob, I bought from Rhode Island and was very happy with the loom I received. Using this loom requires that you remove all the bakelite plug connectors from your old wiring harness and attach them to the new one. Inside the connectors are metal pins - mostly female - that you have to unsolder one by one from the wires in the old loom, then solder them, one by one, onto the new wire loom. It is a bit of a tedious process by I did it over a winter when the car body was off to the body shop. Rhode Island wiring provided an excellent "road map" of where each wire goes and where each wire needs to be in each of the bakelite connectors.
If you don't want to do that soldering work, you would want to specify that with any vendor you are considering.