The vital link: The top driveshaft is an aluminum unit used for Powerglide, Turbo 350, 700R4, and 2004R with a 27-spline yoke. The second unit, also with a 27-spline yoke, is for 4L60E and 4L65E. The bottom prop shaft is a Turbo 400 or 4L80E type with a 32-spline output shaft. In many cases, the transmission you're swapping in for a Turbo 350 or Turbo 400 will have a longer tailshaft than the OE unit, requiring the services of a competent driveshaft shop to shorten (and rebalance) it the appropriate amount (3 inches or less).

Bellhousing Bolt Pattern Identification

Aod Spotter's Guide

Screenshots courtesy of Monster Transmission & Performance.

SOURCE
Monster Transmission & Performance
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