Here ya go:
KMS FAQ
Straight from the horse's mouth.
You need an RM-6057 or RM-6057-SFI and if you use a TKO or 3550, it has to use the short input shaft to work with that bell.
If I remember correctly, the transmission crossmember requires the shorter setup to be used. I could be wrong...
But I know that when I supply drivetrain parts to the Kirkhams, it has to be the short bellhousing & short input shaft setup.