55-57 Chevy Bell Housing

I was wondering why some 55-57 Chevy bell housing have the clutch fork balls mounted threaded on the inside and some are mounted through the outside. Thanks

 

55-56 go in from the INSIDE, 57 go in from the OUTSIDE. There is also a minor difference in how the stater motor bolts to the bellhousing; 55-56 ALL the starter motor bolt holes are threaded, while the 57 housing, the TOP hole is smooth, not threaded. Butch/56sedandelivery.

 

Thank you very much!

 

The 57 had 7/16s bolts securing the rear motor mounts where the 55-56s were 3/8s.