There's probably a simple answer to this, but...on their '56 312 Y-block, how come Ford designates a 9.0 compresson ratio for an automatic tranny, but an 8.4 for standard? (in 57, those numbers are 9.1 and 9.7).

Also...I have read where the baby Birds came stock with a pretty strong Dana 44 19-spline rear end. But in 'The Book of the Ford Thunderbird' by Brian Long, it says that they had a Spicer rear axle with a 3:73 on manual models and a 3:31 on the automatic.

Any input is appreciated. Thanks.