Pulley part number help

[Mr70]

Is that extension number #375123 correct?.It can have two possiblities.

That Crank pulley #3850838-BG was used on:
*1964-69 Corvette equipped w/Small Block & A/C.
*1964-68 Chevelle-Nova-Camaro & Big passenger car series all w/Smallblock & A/C.
*1968 Series 10 trucks w/Small Block & A/C.
The 1970 LT-1 350/360HP engine used pulley #3956668 originally.

Water Pump pulley #3890419-CT was used on:
*1964-66 Big Passenger w/A/C.(Exc. 409 & TurboHydra)
*1965-66 Big Passenger 396-427(exc. Special Hi-perf)
*1966-68 Big Passenger w/Small Block.
*1964-68 Corvette with A/C (exc. Spcl Hi-perf)
*1966-68 Corvette either w/ or w/o Spcl. Hi-perf 327 with A/C & P/S.
*1969 Corvette w/o A/C & or Spcl.Hi-perf.
*1964-67 Chevelle & Camaro Small Block W/O A.I.R.
*1965-66 Chevy II w/327 and A/C.
*1968 Nova-Chevelle-Camaro w/307-327-350.
The 1970 LT-1 350/360HP engine used pulley #3976060 originally.
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