Mod motors are not torque monsters by any means. To be honest I would go old school. 390 FE or a 460 if you want torque.
Now if you want to stay mod motor a little bore / stroke and add a blower don't go turbo. A blower will provide more low end grunt than a turbo will and is instant as opposed to a turbo setup.
All this will require time money and a good tuner.
As far as the plugs, soak them for a day or two, and replace. You should be fine.
the only mod motors that were high on torque were the V10 and the 5.4l for only 331 cubic inches the 5.4l laid out a higher torque rating and better band than the 5.3l did.
unfortunately these engines including the new 5.0 coyote use a small inefficient bore for breathing. to make power with a small bore engine you must add duration to the cams although this raises peak RPM to counter this effect you can add stroke which will drop the power/torque band down while using the same components on the smaller engine to cut costs. this is what ford did with the 4.6l and 5.4l program. to counter the problem with the 5.4 not making enough power/torque for the superdutys they wasted money on the V10 just to share a few parts. this is the term modular!
a rebuild stock cams 2v PI ST headers 75M TB ported PI heads can yield 380ft lbs @ 2600 a 3v 5.4l with ported heads alone can make 410ft lbs @ 3500rpm
adding a turbo or blower will only cost more money yet you'll need to rebuild your transmission.
intake duration is going to dictate where your peak power and torque is made. adding 5lbs of boost from a turbo which is cheaper than blower will yield almost 100ft lbs at 2600RPM. you can easily make 500ft lbs with a 5.4l 2v for under 3k.
for torque I would rather go with a 460 or the 6.2l over any gasoline engine ford has, forget the 390.
