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From: Daven Anderson
Date: April 02, 2001
Generally speaking,the '67-91 LA-318 crankshafts physically fit in '57-66 A-318 blocks. However, the '57-61 A-318's use a different crankshaft flange than '62-66 A-318's. The earlier flange is eight-bolt (later is six-bolt) and the early flange protudes farther out of the block (app. ¾" inch farther) than the later flange.
The '62-66 flange matches the '67-91 LA flange,so for a '62-66 A-318 paired with a '62-up transmission the LA crank will work as a direct replacement.
The LA crank (more precisely,its flange) will not work with pre-62 transmission bellhousings.
You CAN put the LA crank into a '57-61 A-318 block (bearings are the same location),this will require the use of a '62-up transmission (which will fit because the bellhousing pattern is the same) on the converted engine. The '62-64 A-727 is 65 lbs. lighter than the A-413 cast iron ('57-61) Torqueflite,will shift with 57-61 dashboard pushbuttons and is easier to get parts for. I know at least two people who rebuilt pre-62 polys with LA cranks with using the pushbutton A-727 in mind.
By the way,the crankshaft flanges were also changed on the B-series 'big block' V8's in 1962, same as described above (eight bolt to six bolt; flange protusion shortened).