Once again, there are NO dash-1 ZFs that fit a Pantera. The ZF factory built dash-1 ZFs to ONLY fit Mangustas and GT-40s. Early in the pushbutton Pantera series, they built a transition ZF that uses the Mangusta transmission mounted upside-down to a Pantera differential case, with a Mangusta ring & pinion set inside. Almost all these transition ZFs were recalled by Ford and scrapped, so they are rare and parts are very scarce. This box is properly called a "dash 1-1/2" ZF by RBT Transmissions to avoid confusion with the real dash-1 Mangusta/GT-40 ZFs.
Thus there are two different speedo gauges (plus two more with Euro faces), with 4 matching angle-adapters and two different speedo cables. Two combinations of parts will not fit each other and the other two are designed for the 2 possible factory ring & pinion ratios. When you changed gearboxes, you probably kept the same speedo gauge, which for dash-1-1/2 ZFs is designed for a 4.50:1 ring & pinion. The dash 2 uses a 4.22 R & P. On the back of each speedo gauge is a number lettered in green ink. It will be either 1210 giro (for 4.50:1 ring & pinion) or 1610 giro ( for 4.22:1); you need the 1610 and both speedo and adapter need to be threaded the same. And even if you corral all the required parts, if you run rear tires that are different from the stock 26-3/4" OD that were OEM, the speedo will not read correctly. An aftermarket speedo-adapter-gearbox is available from speedo shops to correct such problems but they are not cheap. For other owners who might want to swap ZFs or speedos, all the info (except for the third ZF varient that came in very late GT5 and GT5-S cars with the 'super-ZF and a 3.77:1 ring & pinion) is in the TSBs, Bulletin 1, article 8, published May 26, 1972.