How do I ID a 4 speed, overdrive or not?

C130 Chief said

Weren't OD 4 speeds aluminum cased? Also, they were 76-later. If outside the car they had the larger front bearing retainer.

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Not all were aluminum. The early '76s were iron case. I have one that was assembled in April '76 and has an iron case. Think the aluminum case came on line in June '76. Will agree that if you find an aluminum case 4 speed it will more than likely be an OD. The only way to be sure is measure the bearing retainer. If it 5.125" it's an OD.