Why the C-4 adapter will not fit AOD transmissions:

The C-4 has a removable bellhousing while the AOD does not. The AOD bellhousing is cast as part of the transmission and cannot be removed without machining or a sawzall. Due to the starter being located above the crankshaft centerline on a Y-Block and below the centerline on all engines that utilize the AOD the the lower ear that mounts the bellhousing on a Y-Block engine, blocks the starter opening on the AOD bellhousing.