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As I understand it, the original GT40's ran ZF 5DS 25-O. The dash 1 and dash 2 were put primarily in the Pantera. The dash 1&2 as set up for the Pantera are actually "running upside down" compared to the original dash 0 design. I'm going from memory but I believe the dash 0 had a 4 bolt bell attachment and later versions went to a 6 bolt. 2 people to talk to are; Lloyd Butfoy of RBT transmissions who now owns the rights to the 3 mentioned models.
http://www.rbttrans.com/ Cory Gelhing of Collectors Choice who is a ZF factory certified tech who can preform this operation, and who has prepared many of the boxes for the original cars. Cory Gehling [corycollectorschoice1@tds.net]
Parts for the dash 0&1 are becoming extremely scarce and expensive.
There is a guy that advertises in Hemmings.com who deals in the original GT40 ZF's.
Hope this gets you started.
Andy