A 400 with a set of aluminum heads would do quite nicely... The weight wouldn't be bad, and its pretty hard to argue with a 4" stroke for pulling. Plus they are a smaller footprint than a big block.
A friend of mine did one for his F-250 years ago, standard cam/intake/headers, factory iron heads, with tim meyer zero deck pistons, it's an AWESOME truck motor, big torque at 1200 rpm for pulling trailers, and will still pull hard to 6k RPM when running heavy sweep on rally stages.
Add in the ability to run cheap ZF 5 speeds behind them, and you have a sweet setup...
A recent survay of over 1000 trailer parks in the southeast found the 350 chevy out numbered the mullet by nearly 4:1, draw your own conclusion.