Hi butzie - welcome to DC! I wish I had a recipe for you, but the tacos al pastor I've had here were all served at streetside taco stands and prepared on a special upright rotisserie, with the meat shaved off, like gyros. I don't think this is a recipe you can exactly duplicate at home. But I also did a little googling, and found this site, which gives (extensive) directions for duplicating the taste of this delicious pork, if not the process.
Tacos Al Pastor
Good luck - if this works for you, I might try it too - for a BIG taco party.