I understood the ZF six speed to be a modified ZF five speed. It has a new casting sandwiched between the main gear cluster case and the rear cover plate, in which the sixth gear resides. It will require you to relocate the A/C condensor to the front of the car.
The Ricardo six speed found in the Ford GT is based on the ZF, but an entirely new critter.
By the way, Steve Wilkinson is now finishing up - hopefully for Vegas - a customer car with the GT engine and Ricardo trans. He told me it took major and total rebuilding of the entire rear chassis to get it all in place. First time Pantera owner bought a 98 point car for about $70K and Steve figures the finished car will have every nut, bolt and washer removed/restored and raise the car's cost to about $200K.
The kicker? The new owner intends to make it his daily driver !!
THAT'S WHAT I'M TALKING ABOUT
From Lloyd's website-