Practically speaking, your choices are limited to OTHER Ford-built engines since they all use the same bolt pattern at the bellhousing. Switching to a different brand will require lots more adaption in the area of the clutch etc, just to get it in there. Big-block Chevys were popular in the late '70s among drag-race fans but almost all such Panteras have been converted back to 351-Cs. If you really need a "modern" engine, I suggest a modular motor from Ford- either the injected 4.6-liter DOHC Mustang, or better yet the 5.4-liter DOHC varient, with or without the Lightning-style supercharger.Both bolt up to your very expensive ZF transaxle and the remaining adaptions are relatively straightforward. Interfacing electronics will be the biggest pain, and expens,e but it has been done multiple times so you aren't breaking new ground here. Good luck-
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