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What does SP refer to? I understand that ST = Super Turbine and that the ST 300 and ST 400 had switch pitch converters. If SP means "Switch Pitch" than are you asking if a non-switch pitch can be converted to switch pitch?
In my recent searches, I did find out that the nailhead-specific 400 was available all the way through 1973 in Jeeps and possibly other vehicles (not bolted to nailhead engines) because its bellhousing length allowed room for adapter plates to use with other engines (like AMC ones). Most likely those transmissions were not switch pitch.
I also read somewhere else that as long as the non-switch pitch 400 case takes the early 8-bolt pump, that the passages are there, but one hole has to be drilled to use a switch pitch pump and input shaft. I would guess that all nailhead cases are the early 8-bolt type, since the later 6-bolt type came out post-1973.
IMHO it is not worth the expense to buy the parts to put a switch pitch setup in - torque converter technology has progressed to the point where stall converters that "lock up" with minimal slip are available, rendering the switch pitch obsolete. The cost of such a converter alone would be less than the cost of the switch pitch converter, not even counting the pump and input shaft! Keep in mind that there may be core charges on switch pitch parts.
Either way, good luck.
440shorty
