I bought a harness for my '86 740 GLE a few months back from Nils Sefelt Volvo out of Houston; I checked about a half-dozen places and they matched the lowest price anyone else offered (about 3 or 4 tied for lowest price - I don't recall the others, & have long since discarded my notes). I chose them because they had two in stock at the time & were the closest to where I live; as I recall, the price was in the neighborhood of $320.

They advertise in Rolling; they provide a good discount to out-of-state customers and VCOA members. Call their 800 number, ask for Chuck.

When replacing the harness, take your time - before pulling the old one, study it intently, take notes, account for what goes where, find the corresponding connectors on the new one, etc. (Do this when the engine is cold, and don't forget to disconnect the battery.) When you pull the old harness, this is a good time to clean all connections and get them nice & shiny; use (judiciously) a bit of silicone dielectric grease if you want, to weather-seal the new connections.

The injector wires are not cylinder-specific; I just hooked the connectors on the shorter wires to #'s 2 & 3, and the longer ones to #'s 1 & 2 (this with the injector wires coming up between intake runners for the #2 & #3 cylinders). Also, get a piece of 1/4" diameter plastic split-loom tubing or fuel hose to cover the single wire that loops under the crank pully in case a seal starts leaking.

All in all, it shouldn't take more than 90 minutes.