Hi Hertz350,
IIRC, the 66 GT350 idler arm uses the power steering bushing C3DZ-3356-A, not the manual steering bushing C3DZ-3356-C or C5ZZ-3356-A. That may be part of your confusion.
Why SAI used the power steering bushing for their manual quick steering idler arm has always baffled me. The only thing I can guess is the power steering bushing had a larger ID and OD compared to the manual steering bushing, making it more heavy duty. Any other guesses?
Cory