[Scrounge]

Mopar people are sticklers for originality. Further, you'll have an easier time finding parts for the 318 than a 440, or any other engine that was discontinued before 1980.

That said, I don't know what the resale value of your van would be stock vs. custom. If your van has a 2-barrel carb, it's probably a Holley, which I don't care for. If you want to make it run stronger, the 318 can take a 4-barrel, though, in addition to the manifold, you might also have to change the accelerator cable. If you can find a 1 1/4" Carter BBD, it should be a straight swap, and performance will be a little better. Either way, save the Holley. Your enthusiasm for the vehicle, or your economic situation, could change over time, and having the original parts will be a selling point.

The best book you can find will be a shop manual for your model year, or maybe one from a few years off, since these vans didn't change much over the years. I don't know how much Mopar support there is in Las Cruces, but if there are any swap meets nearby, you might attend one. You might also check the used bookstores, as they occasionally have some decent books in the automotive sections.

 

[Scrounge]

When upgrading for performance, consider that your van is a higher profile vehicle than a car. If your purpose is to take that long hill on I-10 west of town easier, that's one thing, but if it's mostly an in-town driver, you might want to focus on suspension upgrades before modifying your engine.

Here's the small-block rebuild book:

http://www.amazon.com/How-Rebuild-Small-Block-Mopar-Engines/dp/0895861283

This yard had some Mopars when I last went there years ago:

http://www.aupullit.com/

You might call them first to check if they have what you need.