[nxtruck]

71Dragtruck is right; a 327 would have to be very high strung and very high maintenance (expense) to do what you want. A 400, however, could be built fairly easily to make around 550 or so and do what you want to do. It will take a good set of heads, decent compression, and a fairly aggressive cam to do it, though. A big block may be an easier route to go, but if you already have a 400 block, you may want to consider that.
A TH350 can be built to handle the power, but it will need to have about every heavy duty part available to handle both the power and the weight of the truck. A TH400 would be easier to build to handle what your doing with it.
Gear ratio will depend on your tire height, but I would plan on somewhere in the neighborhood of a 4.10 to a 4.56 with 29" to a 30" tall tire. A good converter will be worth the money also.
Good luck with it!