Reply to "How much do the engine + zf move?"

First of all, beautiful workmanship! In my opinion, you should have no movement of the engine or transaxle independent of the substructure. Any movement you encounter would be a considerable amount of torque applied resulting in a twisting movement of the rear substructure; however, from what I see and the way you have the roll cage tied into the rear structure and and again into the cabin, any "torque twisting" would be negligible. The other item which is not depicted in the photo is the cross member between the wheel wells, which will also strengthen twisting action. Many stock Panteras indicate torque twisting with small paint or body cracks where the rear deck meets the rear end above the tail lights. It appears with roll cage and the wheel well metal work, you may be preparing "track time". Lookng forward to progress pictures.