I don't know; have you looked at all the P/N interchages? Here's what parts are common to the '86 Century and '86 Turbo Regal:
Coil, Ignition Module, ECM, EGR Solenoid, TPS, Crank Sensor, Air Temp Sensor, Coolant Temp Sensor, Speed Sensor, O2 Sensor, ALDL.
Here's what is different, but shares a common connection:
Canister Purge Solenoid, IAC motor, ESC.
The Cam Position Sensor may need a new connector spliced in, but shares common wiring to the ECM.
If I already had a TR with a wiring harness in place I would agree. But basically, if you are doing an engine swap using the TR engine, all you need to do is wire the Wastegate Solenoid into the 3.8L Century harness, just like you are wiring the Inlet Air Temp sensor into the '84/'85 TR wiring harness. There might still be some connectors that need to be spliced (like maybe the CPS), but the Century harness appears to be 90% common (as it should be if you compare the ECM pin-outs) and is a lot cheaper from the local junkyard than either a used TR harness or a custom Casper's harness!
I'll be hunting one next week and report on my progress.
Just food for thought;
Dave