360 or 440?

It will be way easier to make streetable hp out of a big block than a small block. For example, building an engine to make 1 hp per cubic in makes for a very easy to live with motor. Plenty of vacuum for accesories, good low end torque where a street engine sees most of its duty, relatively mild idle, good street manners and you shouldn't have to go with a very high stall torque converter.

So the question is, do you want 360 hp or 440 hp?

The only real downside to a big block transplant is the weight over the front end. Look for some big torsion bars like Rumblefish suggests.

Option 1: Take the 360, drop it in the truck and get it running, sell the truck and use the proceeds to build your 440.
Option 2: Take the 360, drop it in the truck and get it running, keep the truck as your daily driver and parts runner. Build the 440 for 1.25 to 1.5 hp per cubic inch and take it out on weekends for cruising or to the track and kick some import butt!