It looks like I'm going to spend my vacation building a TIII for my old '87 Shelby CSX.

I'm a little concerned about wiring it up though. If I had my say, I'd just modify the '90 Shadow ES harness I have for TIII use. The owner would rather use a Spirit R/T harness I have as a donor though. I'm sure I can make either option work, but fitment is a concern to me.

I'm sure I could make the '90 Shadow ES (SBEC) harness fit like a glove, but I'm not so sure about fitting a Spirit R/T harness in a P-body. What have other TIII/P-body owners done?

We're going to rip out the original LM/PM harness and install an SBEC based harness for sure. The P-bodies are really different. There is a multitude of connectors (under the dash) rather than a main bulkhead like most other cars.