[b]Greg:

The Horizon part number SAI50GK93 stack fits all the mid block engines, from the FA-56 up to and including the FA-100.

The big block FA-120 and FA-150 use the SAI120S93, and the FA-180 uses the SAI18093 stack.

For all you small block fliers, sorry. There is no factory stack for you. This is the FA-30 and FA-40A engines.

Bill.