going to respond here without reading all the previous, sorry if it was covered, just going to state my experiences.
I did the 351w swap into a 94 gt from a 95 lightning. I rebuilt cheap with low compression for a future turbo or charger that never happened. Kept al the heavy GT40 upper parts from the lightning, as far as I can remember all that had to be changed was the harmonic balancer, oil pan and maybe motor mounts but not sure if those were necessary. Parts and labor with the help of a buddy of mine were around $1500 if I remember correctly. It was bored over, and matched to the stock T5. It was a torque machine but it was never much faster although I never tracked it before selling it. The tranny did hold up with a pretty good amount of beating.
I did the 351w swap into a 94 gt from a 95 lightning. I rebuilt cheap with low compression for a future turbo or charger that never happened. Kept al the heavy GT40 upper parts from the lightning, as far as I can remember all that had to be changed was the harmonic balancer, oil pan and maybe motor mounts but not sure if those were necessary. Parts and labor with the help of a buddy of mine were around $1500 if I remember correctly. It was bored over, and matched to the stock T5. It was a torque machine but it was never much faster although I never tracked it before selling it. The tranny did hold up with a pretty good amount of beating.