interesting idea, one that i have thought of a few times over the years. the biggest issue though is headers. the 351c is a tight fit to begin with, and stock manifolds dont fit, and headers do barely, but i doubt anyone makes a set these days.
if you want a 351 engine, use a 351w, easier to get, and easier to get headers for.
as for making nasty, my advice is dont. too many compromises have to be made building the car, and driving it, and i dont think you will put up with them for the long term.
now as to a cam, pick one that operates in the 1500-5500 rpm range. its one i think you will be happy with for the long term, especially if you pick parts that compliment the cam, such as a performer rpm or weiand stealth intake, headers with a 1 5/8" primary tube, and a carb in the 750cfm range. i would also pick a set of heads that have a 185cc or so intake runner volume, with a 2.02in/1.60ex valve, and a 64cc chamber.
as for your transmission question, i would go with the 5spd.