My first reaction to all that is that the difference between the 3.5 SOHC and the 3.0 24V is what, about 25HP? That sounds like a lot of work for an improvement of what, 15-20 HP. In which case, it seems to me to be like the turbo swap. That is, if you have to rebuild the motor, and if you can get a swap donor for the right price, then yes go for it, as the incremental costs for the swap itself over the inherent costs of the rebuild are not significant.

Of course I'm talking about myself in the end as I have the 3.0 24V. If we're talking swapping with a 3.0 12V, and even a Gen I to boot, then that may different. Even so, a 3.0 24V swapped into a Gen I would be an improvement that likely wouldn't be that difficult (?).