Posi case

[W Head]

I have a posi case but it does not have the "P" on it. I think GM did not began putting the "P" on the case until 58 or 59, Correct?

W Head

59 El Camino 348-3,2s
59 Impala 409-2,4s

 

[oldskydog]

I have a posi case but it does not have the "P" on it. I think GM did not began putting the "P" on the case until 58 or 59, Correct?

W Head

59 El Camino 348-3,2s
59 Impala 409-2,4s

Nope, it started after April 1, 57. The casting number is what determines whether it was a factory posi case. The posi casting number was 3743833 and the open was 3725899.
The first 57 posi cases in December 56 had a 0 on the 833 case with no X. Then in late jan 57 the 833 case had an X on it until April 1, and later went to the large P on it. Late in 61 the casting number changed to 3789812 but still had the large P.
If your center section case casting ends with 306, it was a 56 open rear.
The open rear cases can all be modified to take the posi and many have been.

 

[W Head]

posi

Thanks Cecil

W Head

59 El Camino 348-3,2s
59 Impala 409-2,4s